Is it possible to change amount of mines in vulture?
1) amount of mines in newly build vulture (instead of 3)
2) amount of mines in a vulture with triggers (when some mines are already used). Note "Modify unit hangar count" does not work for vulture
I don't think it's possible to reload a Vulture's spider mines via triggers. The closest you'll be able to get is just replacing the old vulture with a new one.
As for changing the total amount. I'm not sure. Impossible without modding, and I'm not sure if it's even possible with modding. It's something that would strike me as being hardcoded.
The most recent version of StarCraft that currently supports the Spider Mine total EXE Edit is 1.15.1.
There's a version of FireGraft that supports 1.16.1, and I'm updating the EXE Edits to work with that version. The data.mpq I have uploaded now doesn't support that particular EXE Edit, but I'll have a new one in the next few days that does.
Spider mines, Carrier interceptors, reaver scarabs, hallucinations, broodlings, and other exe edits that alter the amount of said properties were already found for 1.16.1 and listed in this thread: