Welcome to TVPaint Community forums !

Is there a way to retain the Blending Modes (e.g. "Light") of stacked layers with rendering them down to one layer (merging function) ?

yes i too would like to have some sort of 'merge what you see' option.

Agreed!
When using a mix of different blend modes, shouldn't "as seen" be the most common intent for a merge?

and the same goes for picking up a custom brush.
if its set to display it should pick up whats displayed, now it doesn't do that when layers are in blendmode!
(and i have to go through the cumbersome workaround of taking a screenshot)