Modifying magic items.

[Gransoley]

Ok the question is somewhat simple but really specific. Is there a clear rule that allows you to add an effect that explicitly use charges (e.g. wands) to any items.
The specific objective is to make any potion with a secondary effect that uses charges, no matter which effect it is.

[KillianHawkeye]

I'm almost certain that you can't.

[Rebel7284]

My understanding is that the rules imply that you should be able to suggest any custom item to the DM and the DM then determines the cost and requirements to create this item. If the requirements happen to be "10 million gold and crafter must be a rank 2 deity with Craft Artifact [Salient Ability]" then you're probably out of luck, but anything technically CAN be created if you meet the requirements and believe in yourself!

[Gransoley]

Yes i know everything is master approval but I'm doing TO right now I'm not playing. Which is why i asked for specifically this and not similar ideas since they wouldn't work.

[Crake]

Yes i know everything is master approval but I'm doing TO right now I'm not playing. Which is why i asked for specifically this and not similar ideas since they wouldn't work.

If you're doing TO, then you shouldn't be making custom items at all, because any custom item at all is explicitly a DM approval process as part of the rules. All of the item creation guidelines are exactly that. Guidelines, not rules, so you will not find any rules at all to support what you want to do, as no item creation rules actually exist.

[AvatarVecna]

To the best of my knowledge, there is no rule indicating that only wands and staves are allowed to be 50-charge spell trigger items. If you're making one, though, the price formula is going to be the same as it would be for a wand. Conceptually, there is nothing wrong with an item that has both a single-use ability and a multi-use ability. It's maybe a bit weird (to use your example, imagine a regular potion, except the bottle itself is effectively a magic wand), but it's hardly illegal. There's not a default item like that.

As far as theorycrafting goes, using the price guidelines is about as close as you can get. To play on the safe side, the less expensive effect should cost 150% or 200% whatever it would normally cost (so if it's a 10k "wand" and a 2k potion, it should probably cost either 13k or 14k, not 12k). But that's kind of a gut feeling - it's possible it could be added for free without too much issue, the MIC rules on adding new effects to items are a lil vague on what is close enough to not have an extra cost-tax like that.