Can a Paladin use their Divine Bond (Weapon) on different weapons?
For example, if a Paladin primarily uses a long sword and they need to use a mace for undead, can the Paladin call the spirit to enchant his mace rather than the sword?
The only indication of what the bond applies to is this:
Nowhere does it indicate that the weapon must be designated ahead of time.
More importantly, no provision is given for upgrading weapons, something that would be extremely important to detail if the bond was permanent/semi-permanent.
Of course, you could roleplay your paladin as the type who obsessively uses a single weapon (this is my sword). But you can also roleplay him as someone who turns whatever weapon is at hand into an instrument of divine might.