Try giving yourself four different Longswords.
Make them a different magical enhancement bonus each.
So you have a +1 Longsword.
And a +2 Longsword.
And a +3 Longsword.
And a +4 Longsword.
That way, when you want to apply hit and damage modifications to your weapon, you know you're targeting a different weapon each time.
You just need to remember to adjust for the enhancement of the weapon, at the end of the day.
If your actual weapon is +2... you could use that one for the baseline.
The +1 weapon, will need to be one less attack and one less damage, then whatever conditions you want to replicate, because once you're done you'll make it a +2 weapon and you want the correct modifiers after giving it the correct enhancement.
Similarly, you'll need to make your +3 do one point too much for attack and damage, so that when you reduce the enhancement to +2 the bonuses add correctly.
Make them a different magical enhancement bonus each.
So you have a +1 Longsword.
And a +2 Longsword.
And a +3 Longsword.
And a +4 Longsword.
That way, when you want to apply hit and damage modifications to your weapon, you know you're targeting a different weapon each time.
You just need to remember to adjust for the enhancement of the weapon, at the end of the day.
If your actual weapon is +2... you could use that one for the baseline.
The +1 weapon, will need to be one less attack and one less damage, then whatever conditions you want to replicate, because once you're done you'll make it a +2 weapon and you want the correct modifiers after giving it the correct enhancement.
Similarly, you'll need to make your +3 do one point too much for attack and damage, so that when you reduce the enhancement to +2 the bonuses add correctly.