Modify alpha by a layer

[Stefan_l_01]

Hi

I ve searched a lot but I think I do not have found an answer to my problem, so I have to ask:

I originally imported a psd with ~20 layers. They are all "solid" coloured without alpha.

As top layer I´d like now to add a specific layer which adds alpha in specific places. It all gets exported as dds finally, and the alpha becomes later an information for glossy look.

I can not set alpha in all 20 layers below, it must be added as top layer info in specific image regions, so it should add by the layer merge mechanism to the final resulting image somehow.

Is this possible ?

Best regards

Stefan