Well, I have tried. I noticed that the permissions on the app folder looked Linux-like (I *am* a newbie), and eventually figured out how to change permissions (it seems, only temporarily) so that I could copy the new vending.apk to the app folder. Before that, I renamed the old vending app.
So now, I have no access to the Google Marketplace whatsoever. And, the permissions have reverted to read-only. I do not understand.
I wish one of the heavier hitters here could help me out. I'm about ready just to quit.
(Note: I got back into the Nook and just used Linux commands to delete the new Vending & rename the old one to Vending. Now I have the crippled Android Market.)