PatYou wrote
"When I mark the next couple of Bars with the Mass Mover, Finale creates new staves and everything looks weird."
I presume that you mean
"When I mark the next couple of Bars with the Mass Mover AND RUN THE PLUGIN, Finale creates new staves and everything looks weird."
Finale is not supposed to perform any action, just because you select something.
Once you have created TAB with the plugin, you can correct wrong notes by correcting the notes in the standard staff and then run the plugin again. But before running the plugin you should use the Mass Mover Tool to select the region in BOTH the standard staff and the TAB staves. If you only select the region in the standard staff, the plugin will create new TAB staves.
When you have created the TAB, you can move a note to another string with the Note Mover Tool (Use the setting Delete After Merge). And remember: If you have a stem staff with the rhythm notation, you have to hide that stem staff (use Staff Tool) before you can edit the string staves with the Note Mover Tool.
Peter