I don't understand how you will lose settings. This is a completely new install and your old projects with SampleTank 3 will not be affected in the least.
If you'd like to use SampleTank 3 sounds going forward you can point
SampleTank 4 at your existing SampleTank 3 library location (SampleTank 4 now allows multiple library locations) and it will read those and you can go forward that way if you wish.