This is why PF2e made weapon and armour runes transferrable. It also mitigates the problem of getting a powerful magic weapon that nobody can use - just move the runes onto a weapon you’re already using.
This is why I prefer the paradigm of upgrading weapons, rather than just trading them in. An heirloom weapon with a history is soooo much cooler than just some random artifact harvested from a loot table.
You just provide the party with a magical smithing mechanic (flavor to your preference), and whenever they’d find a weapon, it’s a smithy runestone or whatever, and they can use it to upgrade or change the properties of their existing weapon.
Now I can pass down BOTH axes for generations!
Technically speaking, whenever you pick up a new axe, that’s +1 axe.
Just tape them together for double the chopping power.
“Hang on a moment! This isn’t my grandfather’s axe; that one is!”
And my new axe!
Sentimentality is for elves.
