A Wish spell scroll casts the Wish spell. Wish spell can be used to cast an 8th level (or lower) spell without the components it would normally require. If you use Wish this way, whatever spell you use is cast once.
Wish also states a list of particular effects like creating a valuable object, granting resistance, etc.
However, Wish does allow the caster to try and wish for virtually anything. If the caster wants to wish for a permanent "explosion" spell, they can try that. It's DMs call and duty to tell if that works.
From the Player's Handbook:
State your wish to the DM as precisely as possible. The DM has great
latitude in ruling what occurs in such an instance; the greater the
wish, the greater the likelihood that something goes wrong. This spell
might simply fail, the effect you desire might only be partly
achieved, or you might suffer some unforeseen consequence as a result
of how you worded the wish.