Minimum, easiest, least destructive change that "permanently alters" a magazine to hold only 10 rounds?

I have a bunch of magazines for a gun I may sell. What's the minimum change required to make them legal to give to the buyer?

Ideally a change I could make myself that isn't expensive and doesn't risk destroying the magazine if I screw it up

Looking at what's sold with guns now, none of the limits are irreversible with sufficient skills and tools. Looks like requiring tools and skill, or additional parts, would be enough.

So something like epoxy a block to the follower would make it pretty hard to reverse without replacing parts (like the follower).