Editing drawing formats within drawing?

I think the answer is no - formats seem intended to behave exactly like pre-printed formats to ensure that they are not edited, accidentally or on purpose, within the scope of the drawing.

Embedding parameter references in templates is the way to allow variable information into otherwise fixed documents because the reference to the parameter is built in - I believe those parameter references are copied from the format to the drawing, allowing them to be replaced or deleted.

Perhaps you would be better off with drawing templates - these are prototype drawings that have drawing elements already on them and can have a format as a background element.

http://support.ptc.com/help/creo/creo_pma/usascii/#page/detail%2FAbout_Drawing_Templates.html%23

Yes, but the text must be contained in tables on the format.  When a format is applied to a drawing the tables get copied to the drawing.  Once the tables are in the drawing, anything in them is editable.  Just realize that if you reapply the format (same format or a different one), the tables may be deleted and recreated (depending on your selection) causing the loss of any manual edits you have made.  (Hence the benefit of parameters.)