I must admit I thought there was a rule that didn’t allow you to reintroduce a rider in the same season, but I can find nothing in the SCB rules, only can find not being able to reintroduce a rider from previous season not in current line up.
16.3.2 A rider in a Team's declared 1 - 7 at the end of the previous season and not included in that Team’s new season’s initial declaration may not be subsequently re-introduced into that Team without the express permission of the Directors.