I think it could be usefull to have an option, when right-clicking on a layer (and on an encapsulated layer),
saying “set layer to current frame”, which would set automatically the amount to 1.0 on the current frame,
and 0.0 on the previous and next frames, with constant interpoloation (the setting you know we currently
have to do manually). we could then adjust the length of the frame by dragging the previous or next “0.0” point.
Do you understand what I ask?
Is it possible?
I can see that this can be useful.
Those kind of things should be done with a script language.
I don’t believe on add very custom features that applies only for a certain type or style of animation.
I believe it will be good too.
-G
Yep Genete, I understand that script language would suit this kind of automated repetitive task.
But does Synfig support any script language? If yes I don’t know how to write/use it…
I would suggest that these kinds of modifications should probably be done in the Curves panel. Unfortunately, the Curves panel is currently only read-only. So, that’s my useful suggestion… 
G.