Booking the five free excursions

[oskidunker]

Can they be changed later or are they locked in? Is there a fee if you change them?

[mauibabes]

Simple answers for your two Q’s. Yes and no unless you cancel a tour within the usual 48 hours before the tour when you are on board. 
Mauibabes

[LHT28]

O life excursions have to be booked 14 days prior to the cruise 

you can change them up to that point

T & Cs

https://www.oceaniacruises.com/legal/promotion-terms/

 

If you decide later not to do them you could try Destinations services onboard to see if they will work with you to change the tour

 If they have a waitlist  you may get lucky & be able to choose another option

DEPENDS