Can the user edit the details being passed with the link?

Yes, the user can edit the details which are pre-filled. 

If you don't want the user to be able to edit the data, you can make them read-only. 

To do so, append parameters data_readonly=<<variable name>>

For Example:

instamojo.com/SampleUser/SampleLink?data_name=Jerry+Seinfeld&data_readonly=data_name&data_amount=1000&data_readonly=data_amount

Note: You can keep any of the fields as read-only.