The snapshot simply do a capture of an area, not saves the alpha , i already tried.
About the pasters i think is the same problem if i understood you well. All sprites have their efects and blend types. To do that i have to save for each one what blend have and set normal to do the paster correctly and set after the blend mode saved. And well set all the pasters and all correctly with my skills... also will be a big change that how i have set all so before thinking to do something like that i want to test all other ideas.
I think the best thing actually as i said is use only effects. For example the additive blend mode is equal(or very simialr) to the "screen" effect. Maybe if i can know what is the code/script of the blend modes built-in i can replicate them or look how do something similar i don't know.
Because, without canvas/paster, there is no other way or plugin/behaviour to do the same right? At least i not found nothing.
Well, thanks for took your time for reply!, i will investigate and try add various effects to see how works all.