Is there a way of moving all items from a pet's TC collection back into my inventory without abandoning them? I want to rework one of mine but they have over 200 items in their TC and it would take ages removing manually.

As far as I know, nope. It would be lovely, though.

abandoning them isn't going to move the items back to your inventory, before you try anything crazy like that. it just deletes the entire contents of their TC.

it doesn't take that long to remove 200 items. on the TC editing page, hold down the command or control button on your keyboard and click the X on an item; this will cause the updated version of the page to open in a new tab instead of refreshing the page you're on. so if you keep holding down cmd/ctrl you can keep clicking Xes to keep removing items without refreshing the page. since too many loading tabs will slow down your browser, i usually do about 10 items at a time, close all the new tabs, refresh the page, and repeat the process until everything is removed.