need some help with a function

[Gintaras]

Create new function (any name), assign key trigger, eg A, and paste this code:

wait 0 K a
shutdown -6 0 "function name"

It waits until A is released and then kills the specified function or macro, which can be in any command, including waiting.

block and unblock keyboard input of only select keys and not all of them

It is possible using modified BlockInput2. BlockInput2 is available somewhere in the forum. It uses low level keyboard hook, and you can modify its hook procedure to filter some keys.

Or try to use keyboard trigger(s). To enable/disable them from code, use function dis.