We have a Troll 540 which has a BIP and battery charger. Next month we will spend a few days off grid so I fancy buying a portable solar panel with regulator.

Can I safely connect this to the existing battery with alligator clips without removing the existing connections or will it damage the BIP/charger and I’d need to disconnect these from battery first.

Thanks for any advice.

Yes, just clip it on.
I've done that to mine for the last 3 years with no problem although my connection is more permanent using the existing connectors. I then have an inline fuse and run the cable out through the floor and along to a socket at the front of the van.