So i created three custom weapons. The bases were Flaming Long Sword, Dagger of Venom, and a regular Shortsword (it was done for naming flavor and RP since there is not a Wakizashi in the PHB).

So I altered the properties to reflect his approved custom to hit and damage...and here is where it gets funny. 

I added a modifier to ONE weapon to hit.

Modifier: Bonus
Modifier Subtype: Melee Attacks
Fixed Value: 3

It increased all three to hit's by 3.

I added a modifier to ONE weapon that would reduce the damage by 2 so it was:

Modifier: Damage
Modifier Subtype: Melee Weapon Attacks 
Fixed Value: -2

This worked, but it reduced ALL three of the weapons by 2 instead of the single weapon.

So what did I do wrong or is this a bug? Why did it change all of them instead of just the one?

But i want to add only an attack or damage bonus, not both....I would have thought this was possible.

If there is no way to do this,  i am unable to use automated dice rollers (ie: beyond help and D&D Beyond Interaction) or import into Discord and use Avrae. 

Or I just have to toss out the features and make it standard to what DDB says I can use.

You can always just add the custom bonuses to the weapon in the inventory as opposed to creating a new weapon.

You can also add a modifier:

• Damage: type=piercing / the same as the base weapon, fixed value= -2

It's not super pretty, but it does show somewhere. DxJxC solution is probably simpler and more beautiful

Quote from DxJxC >>

You can always just add the custom bonuses to the weapon in the inventory as opposed to creating a new weapon.

 I guess I do not follow you. how would i change the item in the current inventory (base item) without creating a new weapon? 

in one case, the template was the dagger of venom. He had it made as a tonto as he is a samuari. yes, it is just flavoring, however, a perk of the item is that it deals one more extra damage than the regular dagger (it was RP'd out). However, the attack is still the same. 

Quote from Blublabolbolbol >>

You can also add a modifier:

• Damage: type=piercing / the same as the base weapon, fixed value= -2

It's not super pretty, but it does show somewhere. DxJxC solution is probably simpler and more beautiful

 I tried this and no go. it created a whole new attack that you could click on, but we were trying to use this in discord and it wouldn't see the attack right. 

I think in the end, sadly it will just have to be standardized or a manual process. Thank you all for chiming in on this.

Quote from Cee >>

Quote from DxJxC >>

You can always just add the custom bonuses to the weapon in the inventory as opposed to creating a new weapon.

 I guess I do not follow you. how would i change the item in the current inventory (base item) without creating a new weapon? 

in one case, the template was the dagger of venom. He had it made as a tonto as he is a samuari. yes, it is just flavoring, however, a perk of the item is that it deals one more extra damage than the regular dagger (it was RP'd out). However, the attack is still the same. 

 Click on the weapon in equipment - click customize - in "to hit bonus" put 3 - in "damage bonus" put -2 (it may not work on a negative modifier) - in "name" put wazikashi.

Quote from Cee >>

But i want to add only an attack or damage bonus, not both....I would have thought this was possible.

If there is no way to do this,  i am unable to use automated dice rollers (ie: beyond help and D&D Beyond Interaction) or import into Discord and use Avrae. 

Or I just have to toss out the features and make it standard to what DDB says I can use.

If you're trying to use this in Avrae, you can use the command 

!a <attack name> -b <bonus to hit> -d <bonus to damage>

 And if you don't want to type it out every time, alias it:

!alias <alias name> a <attack name> -b <bonus to hit> -d <bonus to damage>

 Also, Avrae doesn't play nice with custom magic items anyway, so you're honestly better off doing it this way.

Quote from Zenog >>

Quote from Cee >>

But i want to add only an attack or damage bonus, not both....I would have thought this was possible.

If there is no way to do this,  i am unable to use automated dice rollers (ie: beyond help and D&D Beyond Interaction) or import into Discord and use Avrae. 

Or I just have to toss out the features and make it standard to what DDB says I can use.

 

If you're trying to use this in Avrae, you can use the command 

!a <attack name> -b <bonus to hit> -d <bonus to damage>

 And if you don't want to type it out every time, alias it:

!alias <alias name> a <attack name> -b <bonus to hit> -d <bonus to damage>

 Also, Avrae doesn't play nice with custom magic items anyway, so you're honestly better off doing it this way.

 This is good to know. seems Avrae has many hidden features or ones that are not easily found.

Yeah, the help menu isn't the best design, but it's just about as good as you can really get it in something completely text-based.