Vans might be colaberative.
If you want it and are willing to pay for the engineering, Van has probably already done the preliminary design review, and possibly has some parts drawings.
Vans already has a product liability waiver on the kit. If you mod it, the kit becomes less like a Van's, and less likely to breach the boilerplate.
If you want to use a profesionally engineered TW conversion to Van's RV-10 kit, I see a few choices:
1; Call Van and ask if you (or your group) can pay to have him do it.
2; Hire a builder in good standing who has your confidence (credentials whatever) to contact Van and present your groups proposal for Van's review.
3; Hire a designer and go it as an individual or group without Van.
4; Do It Yourself and wow us at the fly in.
And of course; The American answer, "All of the Above"

All of those roads have been travelled.
1) The RV-9 was not initially offered. Van designed it due to oral demand, but said that so few were sold that it didn't pay for the effort.
2) Van gets some requests to check out mods to his plane, like the tip up/slider canopy, etc.
3) I'm thinking of the Rocket, Harmon and Fredricks.
4) Fastbacks, Retracts, alternate engines etc.
__________________
Scott Emery
http://gallery.eaa326.org/v/members/semery/
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is
nothing-absolute nothing-half so much worth doing as simply messing around with
Aeroplanes
(with apologies to Ratty)
2019