((Thanks for your answer… deleted because I’m paranoid))
Alimony in a Consent Order is modifiable, and in an Separation Agreement it is not. It seems that you all have a SA, so she is legally stuck on the amount of alimony and it is up to you if you want to be kind to her or what you want to do.
You cannot deduct the voluntary support- per the IRS alimony must be pursuant to an SA or court order to be deductible. If you pay above what is in the SA, or your SA doesn’t provide for alimony, then it will not be deductible. You are not setting an precedent though- the SA is binding on her (in the sense that alimony is over- assuming of course the wording of the agreement states that alimony has terminated and there are also the proper waivers) and she cannot come back and use your kindness as a way to wriggle out of the SA to get more or continued support.
So long as you do not put anything in writing, you then can end the “voluntary support” when ever you like- if you do a new agreement you can condition the termination on whatever you want.