Can I change crowdfunding deadlines?

Try not to extend deadlines. 

Only in highly exceptional cases, one could extend the deadline of a funding activity. A deadline of a funding activity can, in no circumstance, be changed after the original deadline has passed. Once the deadline passed, a payout was created. If a funding activity is being reopened after the deadline, the system is disrupted and the amount that is raised at the deadline will be paid out. This causes that the rest of the money raised, falls between two stools.  

Regarding task activity, deadlines can be adjusted in the back office. Be aware of email triggers related to deadlines.

Why not? 

We are legally obliged not to keep donated money for longer than 60 days.