Redesign UserForms in VBA project with VB tools

Need help moving a Word VBA project toward VB. In particular, the User Forms in VBA are very limited and 'blocky'. My customers complain how ugly my forms are in this modern age.

Can nicer forms (I have dozens that need improving) be designed in VB (or other language) and be called into the VBA project, similar to the way I currently call in a User Form? I will want to preserve as much of the VBA module code as possible (it's a half-million lines long and does a lot of stuff). I need the project to continue to run as an add-in to Word.

(I don't even know if I am describing it correctly, but hopefully you can make sense of it.)

The underlying project is Pathagoras found at Pathagoras.com if you want to take a peek. Not an urgent project.