It's possible to have more than one HD account from different seeds in a single instance of Mycelium wallet.
In Accounts, click the key+ symbol, go to Advanced.
The text there says "to add a Single Address Account," but I think you can add an HD account.
There was a post by dooglus in this thread about it many pages ago.
I did it on one of my devices a while back.
I just tried it, but it created only a single-address account. Perhaps the function has been removed, because it could confuse newbies.
But even if it worked, if you wanted to draw a line and erase the entire past, you would also have to forget your Local Trader history and identity. I believe, to do that, uninstalling and reinstalling Mycelium is the way to go. Just be sure not to erase an account before emptying it.