Yes. After confirmation of your request by the Dean of the undergraduate program, in view of your cover letter, your choice of master will be shifted in the following year.
If you did not make a final choice regarding your gap year, you must put as a first choice the programme you want and as the second choice the gap year.
No. You can only benefit from one gap year during all your studies.
Yes. You must send a cover letter to the administration of the Undergraduate Programme - email@example.com et firstname.lastname@example.org - describing your motivations to do a gap year, before 12th May.
Yes. You must pay 25% of your tuition fees for the Undergraduate Programme to retain your status as a student of Sciences Po.