Currently if you use this snippet from the GiveWP snippet library: https://github.com/impress-org/givewp-snippet-library/blob/master/form-customizations/populate-amount-name-email-from-url.php

When you visit a form that pre-poulates everything correctly, switching to a different gateway on that form causes the data to drop out that was prepopulated.

I'd expect that data to persist in the same way that manually entered data persists.