Overwrite annual leave request with sick leave

Hi, we need an option to overwrite an approved leave request with sick leave days. Our employees can apply for sick leave even while on annual leave, and in that case, those specific days are subtracted from their sickness allowance (not leave allowance). Right now, if e.g. employee has annual leave Sep 1 - Sep 15, and then gets sick and wants to apply for sick leave on Sep 6 - Sep 10, we have to modify and split the annual leave request in two pieces (Sep 1 - Sep 5, and Sep 11 - Sep 15) to be able to add this sick leave in between.

Things get even more complicated if the employee would take sick leave on e.g. Sep 3, 7, 12 (for med exams and check-ups).