How much flexibility do you allow with enchanted item lab texts? Say someone creates a wooden medallion that, if tapped three times, casts Gift of the Frog's Legs upon the wearer. Would you allow the lab text to be used, or give a bonus, if the caster created another item that changed any or all of: method of invocation, shape, material?
I guess I am wondering if the lab text is for the effect on its own, or is it for the effect, method of invocation, shape and material.
Canonically "no features of a spell or enchanted item effect may be changed". In particular, shape and material must stay the same: "the item itself must have the same shape and material as the one described in the text". We keep it that way in our games.
As for varying the method of invocation ... technically you could create an elaborate method of invocation that makes the item activate on any repeat of the action taken between the first and the second utterance in the presence of the item, ever, of the word "Urdublugub". So you say "Urdublugub", then "record" the activation method, and when you are done you "lock it in place" by saying "Urdublugub" a second time. So we tend to be flexible on that, unless the creator of the original item did not want any flexibility. You know, there are magi of Verditius who really insist on all copies of their Wand of Ultimate Power to be activated by the sentence "Praise be given to Arrogans of Verditius, mightiest of enchanters!".
Of course, anything like environmental triggers, restricted use etc. must stay the same as in the original item.
I run it so that everything has to be the same, including command word. This has become a plot point, because many of the grogs and companions wear shirts with Doublet of Impenetrable Silk activated by a command word. This has been observed enough by other covenants that everyone knows about it. So when the grogs put their hand on their chest and say the word, rivals and enemies present all know they're prepping for a fight. It's like saying "Shields up, captain."
No. None of it can be changed in any way. If the original wooden medalion is made from oak and painted white with a lead-based paint before or during enchantment, guess what color any copies must be.
The only thing that it might be possible to vary (my troupe certainly ruled that it was), is if the device is designed for a specific individual (with regards to Warping). Your troupe may rule that the same labtext could be used to design a otherwise identical object, with a new "designated user".
What about a lab bonus for creating a similar item? Say a metal medallion instead of a wooden one, Would you offer up a small bonus for "similar spell"?
As far as a bonus, I have always allowed it to count like creating a new spell, i.e. +1 per ten levels of effect. This encourages improvement without pigeon holing the magi.