Is it possible to change values relatively in automation?

I set a cutoff param to 64, and used automation to change it to 127.
If I change the param to 100 at this point, the sequence will still play the parameter from 64 to 127.
Is there any way to get automation from 100 to 127 without rewriting it?

Off course not. Not in a generic way.

If it's a virtual synthesizer then maybe you can automate the modulation wheel depth modulating a cut-off instead of the cut-off directly, so it would in a relative fashion.

That's a good idea. Thanks!

I cant really say if this would work flawlessly in your situation, but something I like to do is have a track with just a set automation parameter. In my case if I want the plugin to stay at mono but be able to switch presets without having to constantly set voices to mono I will dedicate a track to just setting the voices. I also use separate tracks for things like pitchbend and modulation so I can try different things. You could probably set your base parameter in this track then use another track to modulate.