Help Understanding Portfolio Loans

Can someone with experience with portfolio loans help me understand how they work. For easy numbers example, if you have 10 properties in a portfolio loan and their value is $100k each and you get an 80% LTV portfolio loan for them of $800k. Are you able to sell a property within that portfolio loan? I assume if you can sell a property within that portfolio loan, the bank is going to require the principal from that loan paid down since that principal will no longer be secured against an asset that you own. Does the bank start the portfolio loan with a ledger of each individual property and their respective value? Also how are principal payments disbursed evenly across properties during normal monthly payments?

Is my thinking correct for my example above: $800k loan. You sell one of the properties for $120k, you would need to pay down $80k minus any principal paydown to date of the original properties principal balance.

Thanks in advance. Sorry for the wordy question!