Select what to import using Migration Tool

I'm in the process of migrating from IPP using the tool and would love to be able to select what I want it to import - particularly pay components. Components don't migrate as you would expect (for example Salary comes over as a custom code) and you can't delete a custom code without individually removing it from every employee and current year user first. Would much rather not import the pay components (pay codes) at all and start again afresh!