AttemptUndertook Okay, I just did it today and it's successful. I had a separate tablet. I backed up my original molly account and restored it on the tablet and then the tablet was the main account and then you can add 4 extra devices/profriles as you want. Molly , molly Foss, molly beta, signal, signal desktop, signal foss all good.
One device is the "main" and it shouldn't be your phone. You will have to relink all the other instances but all my data transferred and we are good.