I don’t need the priv key for my counterparty wallet,
There’s no private key for the wallet, there’s a pass phrase (also there is Easy Access key - see FAQs)
And is it possible to change my pass phrase?
No.
I need the priv key for 1FK32eU7srjwjV9HfGsNL1aaDKJXHbRDDu which is the address holding my tokens.
If the answer provided by p* is not easy to understand, check out the FAQs.