I don't think it's possible as traps' type is most likely calculated only based on its coordinates and them only. Other way it would be illogical for trap patterns to exist at all.
EDIT: Now that I've seen Thomas' post I think you are right. As now it's possible, it should be done.

Upvoted. Right now the B/U/C status of these wands makes absolutely no difference, right?

This is a great idea to rebalance the lack of trap patterns! It makes more sense than previous behaviour, without altering the gameplay too much.

I'd be wary of allowing teleportation traps - it would be a little powerful, and encroach on teleport wands, but other than that I agree!

This is a rather peculiar suggestion, in as much as I'm aware B/U/C of wands don't have different effects. Please correct me if I'm mistaken.

This isn't really a different effect - it still creates traps, just better. However: cursed wands of wish fail 50% of the time, cursed wands of knocking lock doors, rusty wands of lightning can electrocute player. There's precedent for differentiation of wands due to their status.

Well, the whole concept doesn't work from a sensible point of view.
How does the PC get the wand to create a specific trap? Does he/she zap the thing and the wand queries the PC or does the wand have to be handled differently for each type of trap the PC wants to create. Even in that case where does the PC gain this special knowledge of getting the wand to create that specific trap? A blessed wand can also be un-identified, so does the PC just do that specific ritual with every un-IDed wand hoping that maybe it is one of trap creation.

This was my first thought too. Wands of trap creation would basically become equivalent to wands of teleportation with this change--even better, in some ways, because the trap is persistent.

[edit]*shrug* same problem kind of already exists for wands of far slaying and wands of wishing. I suppose you could have it that the unID wand always produces a random trap, though that would not be consistent with how unID items typically work.

So, the wand queries the PC. :p

Actually, I'm starting to like this suggestion it will give some nice extra options in some difficult areas.

Maybe the Pc waves the wand in the air, and it starts making a stone block in the ceiling? Wave it at the wall, and it starts drawing an explosive rune... Wave it at the ground and a hole starts to appear. I'm imagining that the player kind of 'makes' the trap by drawing it with the wand.

Myself, I still love the idea of dismantling traps into their component parts (with disarm traps) and re-creating them elsewhere (with a chance of failure). Earlier today I suggested having it integrated into the wand of trap creation, but maybe having a non-magical 'trapping' skill as a separate RFE might be a more appropriate suggestion? :)

I suppose TP traps are a problem. They maybe could be removed from blessed version? Unsure.

Maybe different types of traps could take a different number of charges? Or you have to use a certain number of HP/PP to create a trap that depends on the type?

On the other hand, this would make this a pretty complicated mechanic for one wand...

So, blessed wands of monster creation and wonder should maybe also make you choose the monster and spell? Why stop at trap creation? Just make certain monsters/spells use more charges or PP+HP.

The PP cost solution is leaving low PP characters at a disadvantage again and they are probably the ones that use wands more than spellcasters.

I don't know, this is too OP.

Surrounded in the end game when you have fire resistance? Just create fire trap under your feet and activate it repeatedly for free fireballs. Or teleport away. Or surround yourself with alarm traps.

That's too much power for wands that normally come with a lot of charges.
I suppose we can make it non-rechargeable (like death/wish) to balance that.

I don't think it's too OP when you have to bless it. I consider it a roughly fair tradeoff to moving a few paces to get the desired type. Also fire traps run out after a few triggers.

One blessed water is nothing. It's not just fire traps. I can now also keep gremlins at bay, create 5+ acid traps in a row or acid alternating with flash traps, alarm traps in cavernous areas, etc

"So, blessed wands of monster creation and wonder should maybe also make you choose the monster and spell? Why stop at trap creation? Just make certain monsters/spells use more charges or PP+HP."
Wands of wonder and wands of monster creation are both already quite useful (although monster creation aren't fantastic, they have very powerful niche uses). The issue with trap creation is that the wands used to be excellent utility devices, and we *lost* the ability to select our trap type (and with it, a lot of strategies) when top trap type was randomized in 1.2.

I do think it's somewhat overpowered to let the player choose from all trap types... but I like the idea of blessed wands of trap creation giving the player a choice. Same with monster creation (wand of wonder is completely random for a reason, of course).

So here's an idea for a way to make it just that little bit better, without making it too overpowered: give a prompt where the player can choose between two traps/monsters, chosen at random from the available options. The keystrokes required to choose could simply be up and down, or left and right, or whatever other pair of letters people think are appropriate. So it would go like this: "Do you wish to make a...", and then provide two options. A casting is used up by the time you get to this prompt, so cancelling wastes the casting (alternatively, you're forced to choose one of the two options, no cancelling).

By having two options with a blessed wand, you get just that little bit more control, but you can't just choose to make a teleport trap or blink dog on your first cast (unless you're lucky).

A similar thing could perhaps apply with the wand of ball lightning - if it's blessed, you can select a direction, but it only skews the probabilities (say, 30% chance of casting in chosen direction (eg/ L), 20% chance each in the two adjacent directions (UL,DL), 10% chance each in perpendicular directions (U,D), and 5% in directions adjacent to opposite direction (UR,DR), with no chance of it firing in opposite direction (R)), rather than turning it into a regular wand of lightning.

Well, TB thought that even pit+blanket desired trap creation was too exploitable that he went so far to randomize trap type. Besides I've hardly ever used top trap type exploit( only in DF) and I still use this wand in the current version versus cats or EG with it being randomized. Much more than wands of monster creation or wonder.

"So here's an idea for a way to make it just that little bit better, without making it too overpowered: give a prompt where the player can choose between two traps/monsters, chosen at random from the available options. The keystrokes required to choose could simply be up and down, or left and right, or whatever other pair of letters people think are appropriate. So it would go like this: "Do you wish to make a...", and then provide two options. A casting is used up by the time you get to this prompt, so cancelling wastes the casting (alternatively, you're forced to choose one of the two options, no cancelling)."

I really like this! Good call!