This suggestion might sound weird BUT!!!
Have you ever shared/wanted to share one topic together with your friends? Having one shop for the lions? Or simply having main and side - and having 1 shop for both account lions?

I sometimes do not log in to my main/side, still sell lions and... can't update the topic just because I don't want to log in. I find this annoying. People start asking for lions that already are sold, and you can't update, because you have decided to skip this week of playing via that account.

My suggestion: Allow more than one ID to edit the thread. Maybe to main and side, or maybe to even more users, by typing them in a field and clicking "allow editing" or such. As well, give option to remove such IDs.
ONLY the creator of the thread would have this add/remove option, whoever was allowed to edit the topic can not use the add/remove options.

I do believe this would make the usage of threads even more comfortable :)
If you feel unsafe about allowing some person edit your thread - do not add that person, or simply save the text into some text file in your computer. IF annoying mess up happens, simply restore to previous version and remove that ID away.

This can be very useful to use the thread for your both accounts, various sales, advertisements, roleplayers :)