I want to create a Quarterstaff that does only one point of damage.  Is it possible to change the damage amount for a given weapon type?

No, but if I may ask: why do you want to do that? (There may be another way to achieve what you're ultimately trying to do.)

Quote from wagnarokkr >>

No, but if I may ask: why do you want to do that? (There may be another way to achieve what you're ultimately trying to do.)

I figured as much playing around with the Create Magic Item tool, but thought I'd ask.  So here is what I'm trying to do.

The Kobold Inventor has the following item.

Scorpion on a Stick. The kobold makes a melee attack with a scorpion (see the Monster Manual) tied to the end of a 5-foot-long pole. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 1 piercing damage, and the target must make a DC 9 Constitution saving throw, taking 4 (1d8) poison damage on a failed save, or half as much damage on a successful one.

One of my players has now acquired Scorpion on a Stick and wants to use it as his main weapon for a while, so I thought I'd create it for his character sheet. The base weapon I want to use is Quarterstaff, but based on the item's description, I'd like it to do only one point of damage.   

The truth is that leaving it as a Quarterstaff with the extra feature is fine, and just telling the player that it only does one point is the easy solution. 

That is hilarious, and I love it.

One thing you can do is make a custom attack on the character sheet itself (via the "Manage Custom" button in the Actions tab). You can put in a fixed value of 1 for the damage. However, it will still add the wielder's ability modifier (presumably Strength for a quarterstaff) to the damage, so it will only actually be 1 if their Strength is 10 or 11. Perhaps that's reasonable for a player character, though.

Quote from wagnarokkr >>

That is hilarious, and I love it.

One thing you can do is make a custom attack on the character sheet itself (via the "Manage Custom" button in the Actions tab). You can put in a fixed value of 1 for the damage. However, it will still add the wielder's ability modifier (presumably Strength for a quarterstaff) to the damage, so it will only actually be 1 if their Strength is 10 or 11. Perhaps that's reasonable for a player character, though.

 Yeah, the Kobold Inventor in Mordenkainen Presents: Monsters of the Multiverse has a lot of 'unique' gear.

You can reflavor the Blowgun. It's the only weapon that I'm aware of that does 1 damage. Give this a read on the things you can and can't change when customizing weapons.

The only problem with using the Blowgun in this specific situation is that it's a ranged weapon, which means D&D Beyond will use the character's Dexterity for the attack roll, which wouldn't be correct for something that's essentially a Quarterstaff, unless the character is a Monk.

True. You could add the finesse property and it would use the higher of the two which would catch any PC that has their STR higher than their DEX. I'm not aware of a way to force STR rolls if DEX is higher.