Can I make a continuous, togglable, deactivatable belt of enlarge/reduce person?

Question

If you are using a magic item, say a belt of enlarge person, is it possible to deactivate it without taking it off or using dispel magic?

The only kind of ruling that seems to come close is for weapon properties such as flaming where they can be turned off (in case you are facing something which heals with fire damage).

Basically my end result is I want a belt with two spells, enlarge person and reduce person, and the ability to switch between them as desired, likely with a command word. Would such a belt be possible?

I want a continuous effect, not command word as I would have to activate it every minute. A belt that has a continuous effect, but a choose-able continuous effect from a menu of two options plus a third option to have neither on.

Answer 1

So a belt can be a wondrous item that continuously applies. This is a pretty standard type of magic item, explicitly addressed in the Estimating Magic Item Gold Piece Values guidelines. The guidelines for that kind of item is:

spell_level × caster_level × 2,000 gp × 2

Where the ×2 multiplier is due to these spells having a minute/level duration.

Both enlarge person and reduce person are 1st-level spells, which means that (with caster level 1st) either effect could cost as little as 4,000 gp by the guidelines.

There are also guidelines for combining effects: any effects after the most expensive one cost 50% more than they otherwise would. For that caster level 1st version, this means we have:

2,000 gp + 2,000 gp × 150% = 7,000 gp

But by default, enlarge person and reduce person cannot be applied at the same time; they cancel one another out. So these effects have to be continuous, but able to be turned on and off.

Command-word items are another kind of wondrous item, which allow you to use a spell effect at will, by using a standard action to activate it. These are usually cheaper than continuous, since you need to re-use that action every so often. Many weapon effects can also be toggled at will, again as a standard action. So turning either effect on or off is likely a standard action. However, this kind of thing is not handled by the guidelines.

Personally, my feeling is that this feature is necessary to make enlarge person and reduce person work together, so it is basically a part of combining those effects. Adding additional cost to make them usable seems pointless.

Extra features, like allowing you to go straight from enlarge to reduce or vice versa, or to toggle more quickly than a standard action, would cost more. Quite a lot more in the latter case; if it was a swift action, that would effectively be quickened rapid enlarge person or quickened rapid reduce person, 6th-level effects. That would cost a staggering 660,000 gp.

So what does it actually cost?

The guidelines are just that, guidelines. Becoming Large or larger is quite valuable (and Small or smaller has its merits, though it’s less significant), so the base 7,000 gp seems very low to me. Permanent size changes are rather rare; for example, you can’t get it as a feat. Races that get Large size with “only” LA +1 are considered very good. It’s very difficult to establish the value of an entire level like that, but I’d say you’re looking at easily three to five times the guidelines’ suggestion (i.e. 20k to 30k).

The 660k of the swift-action version, on the other hand, is too much. It’s good, but it’s nowhere near that good. Probably a tenth of that (66k) would be enough.

Answer 2

In general, new magic items can do whatever you want (pending DM approval).

Magic items do lots and lots of weird things that aren't precisely accounted for in the magic item GP value table. New magic items (and their prices) must include some level of human judgement, and the most important thing is that the benefit that you get is roughly equal to the cost that you pay.

If what you want is a belt that lets you switch between regular, reduced, and enlarged with a standard action, then you can do that. The magic item creation GP price table is meant to be a guideline, not a hard limit on exactly which magic items you are allowed to create:

The easiest way to come up with a price is to compare the new item to an item that is already priced, using that price as a guide. Otherwise, use the guidelines summarized on Table: Estimating Magic Item Gold Piece Values.

There are many items that do things that are not simply replicating a spell or providing a standard bonus. As long as the gold price that you're charging isn't too low for the power that you're getting, you can make whatever magic items that you want, pending DM approval.