Yes, that is possible for MSc mentors! We are looking forward to welcoming you twice this summer! If you want to be a MSc mentor in both AIDs, you can mention it in the comments of the registration form. The registration fee will be the same as for one AID.
For BSc mentors you can also indicate it in your registration form, but you will be put on a waiting list at first. If we have a shortage of BSc mentors, it will be possible to be BSc mentor in both AID's.