Can a canthoplasty be slightly loosened? (Photo)

You look good at this point.  Every time you  go back in here surgically, you run the risk of more issues.  It is a tough area to get perfect as there are many vectors of pull working at the same time.  So I would be very cautious of doing anything else.  With time it will relax more and the tight feeling will resolve. If you go in to cut the canthoplasty you may be back to where you were pre-op.  

Your photos show an excellent result and you should consider whether you want to risk disturbing that result for a minor improvement, that may improve on its own over time.  Each surgery creates scars which can be unpredictable in how they heal and the effect they cause.   I recommend not doing anything, but you should have a very detailed discussion with your surgeon about whether your issue could be improved without creating another issue.

You will need a very careful consultation to determine what precisely your issue is and why you want the lid "loosened."  The tightness may be related to tissue tightness, dryness, or possibly something else.  It would be bad to have a surgery that destablizes the eyelid but does not solve the problem.  What does your original surgeon say?