%%wppa%% is catched by a filter (if it is in a page or post, not in a textwidget) that replaces it with php code that does all the dirty work. The filter also 'sees' things like %%album=.. %%size=.. etc. See wppa_filter.php.
The most important part is the call to wppa_albums() that does the insertion of the theme file wppa_theme.php.
You may call wppa_albums() directly from a page template and specify what you want, either by giving the appropriate arguments, or by setting a bunch of globals to the right values.
For more information on this topic see My Docs&Demos site, especially the wppa_albums() documentation.
This was lesson one.
As i am working on this plugin - almost every day - for over a year now, so i rather good know what is possible and what not.
Also: I like enhancement requests. They are responsible for let's say 80% of the current functionality.
So, please tell me what you want, there is a fair chance that it is already possible. New things i tend to implement within one or two days if they are not too complicated. Also, it would take you much too much time to learn about all the ins and outs of the code.
Further, do NOT change any code exept for what and how it is explained in the documentation, it would block you frm updates.