cancelling Excalibur?

[(K. Bruner)]

Before I spend the rest of my virtual life trying this, can someone tell
me if it's possible to cancel the enchantment on Excalibur +5?  I want to
improve it, so I keep casting a spell of cancellation on it and it
doesn't budge.  I know it's protected against magic, but doesn't that
just mean it's less likely to be affected, rather than never?