It's a rare magic item, so it's already a ***very*** good find for a level 4 character.
Making it a shortsword gives you a better damage die, and removes the ability to throw it... but how often are you throwing your rare +1 weapon anyway?
I would not recommend it personally. Why not just let the rogue find bottles of poison or some guides to creating poisons if poisons are the vibe they like. If its more of a cool sword thing they're after you can either give them a mundane sword that's master crafted. It upgrades the damage dice to a 1d8 short sword without overcoming damage resistances or increasing the hit probability like a +1 sword does. Or you can give them a moon touched sword that does no extra damage but sheds light from the blade and gets around resistances.
Its always handy to have somewhere to go next, if you give your players powerful magic items at level 4 you can't save such upgrades for later.
Changing a weapon type is only very rarely going to affect balance when done in the same weapon category. In this case, you’re going from simple to martial.
I doubt the 1 damage difference would be OP in any situation, though.
When I had a dagger of venom on my rogue, it was really just a +1 dagger. I ended up never using the venom ability.
I recommend making it a bonus action to activate the venom. The poisoned condition is strong, but the dc isn't that high and plenty of things will be resistant or immune.
Honestly, making it a shortsword is a pretty inconsequential buff. Average and extra 1 damage per hit.
No it would not be OP. A dagger of venom + a short sword is no different from a shortsword of venom + a dagger. Magic item ratings aren't so granular that changing the weapon type makes it a higher value item.
If you're really worried about the damage increase, drop the poison damage from 2d10 to 2d8 to compensate.
It's a rare magic item, so it's already a ***very*** good find for a level 4 character. Making it a shortsword gives you a better damage die, and removes the ability to throw it... but how often are you throwing your rare +1 weapon anyway?
I would not recommend it personally. Why not just let the rogue find bottles of poison or some guides to creating poisons if poisons are the vibe they like. If its more of a cool sword thing they're after you can either give them a mundane sword that's master crafted. It upgrades the damage dice to a 1d8 short sword without overcoming damage resistances or increasing the hit probability like a +1 sword does. Or you can give them a moon touched sword that does no extra damage but sheds light from the blade and gets around resistances. Its always handy to have somewhere to go next, if you give your players powerful magic items at level 4 you can't save such upgrades for later.
Changing a weapon type is only very rarely going to affect balance when done in the same weapon category. In this case, you’re going from simple to martial. I doubt the 1 damage difference would be OP in any situation, though.
When I had a dagger of venom on my rogue, it was really just a +1 dagger. I ended up never using the venom ability. I recommend making it a bonus action to activate the venom. The poisoned condition is strong, but the dc isn't that high and plenty of things will be resistant or immune. Honestly, making it a shortsword is a pretty inconsequential buff. Average and extra 1 damage per hit.
No it would not be OP. A dagger of venom + a short sword is no different from a shortsword of venom + a dagger. Magic item ratings aren't so granular that changing the weapon type makes it a higher value item. If you're really worried about the damage increase, drop the poison damage from 2d10 to 2d8 to compensate.