So, after 12 years of membership, a LOT of the cards I've bought in the past are no longer available. Are replacements, either for free or at discount, available?
Also, I just re-downloaded the app, but it gave me a new id and lists me as a new member -- how do I change it to my actual membership ?

Also, I just re-downloaded the app, but it gave me a new id and lists me as a new member -- how do I change it to my actual membership ?

Click on settings (the cogwheel icon)
Enable Advanced Settings
Click on Login With Another Account
Enter your old account details

Then. if necessary, click on rebuild collection
Then, if necessary, download your cards

If you still have the contents of your old Data and Models directories you can copy the card data from those rather than having to download them again.

If you have previously bought cards that have since been withdrawn you can't download those cards but if you contact Totem they will refund their cost in credits.