The tip type and dispense mode drop-downs are just filters for the Liquid class input so they can’t accept variables. However, you can put a variable into the Liquid class input that uses any tip type or dispense mode which bypasses or overrules whatever is set in the filters.
So you can leave the filters as the default and assign different liquid classes representing different tip sizes, modes, etc. Just be sure you use the right tip size sequence and volume range, which can also be set as variables! 