I'm not sure if this would change the tooltips correctly as you are expecting but the following adjustment code can be copied/pasted into a personal .user file or if the community wants to borrow it into their adjustment files. It has two dropdowns - the first looks for a weapon that must be in inventory, the second asks for the overriding attribute.
Code:
<thing id="pXXWepAttr" name="Override Ability Modifier for Weapon (Attack and Damage)" description="Override the ability modifier for a weapon attack." compset="InPlay">
<tag group="OthAdjCat" tag="Equipment"/>
<tag group="Helper" tag="NoIncr"/>
<tag group="Helper" tag="AdjNoPlus"/>
<tag group="Adjustment" tag="YourWep"/>
<tag group="Adjust2nd" tag="Attribute"/>
<eval phase="PostAttr" priority="10000"><![CDATA[ ~ If we're not enabled, get out now
doneif (field[pIsOn].value = 0)
~if nothing's been chosen, get out now
doneif (field[pChosen].ischosen = 0)
doneif (field[pChosen2].ischosen = 0)
~ Pull selected ability tags
perform field[pChosen2].chosen.pulltags[DamageOver.?]
perform field[pChosen2].chosen.pulltags[MelAttOver.?]
perform field[pChosen2].chosen.pulltags[RanAttOver.?]
~ Push them on to weapon
perform field[pChosen].chosen.pushtags[DamageOver.?]
perform field[pChosen].chosen.pushtags[MelAttOver.?]
perform field[pChosen].chosen.pushtags[RanAttOver.?]]]></eval>
</thing>