Sheldon, in my line of work, providing that type of service is called consulting, not technical support. I don't think it's reasonable to expect that you would provide free technical support to someone who wants to modify your product. If you did so in the past, I would say that was an example of extreme generosity, the type of service that has earned you a reputation for providing world class products and support, to be sure. But it is not something that is economically feasible nor sustainable unless you build it into the cost of the instruments. And since not all users want to mod their instruments, I don't think you should do that, because it wouldn't be fair to the majority who are happy enough to leave well enough alone. (Would I like to put a PTone into one of my NG-2's? You bet! But if I do, I will buy the pickup from you, and I'd buy a pickguard if one were available. But I'd assume that I'm on my own from that point on.)
At the risk of getting flamed by all the other happy customers who have been so lucky to benefit from that free assistance in the past, and those who were hoping to benefit from it in the future, I would suggest that they should either obtain that type of assistance from their dealer, their luthier, or the public support forums. I think that they all (I should say WE all, since I am included in that group as the happy owner of two Dingwalls, with a third on the way), should be happy to leave you alone to do the important work of incubating those puppies and getting them out the door!!!
To finish out on the consulting topic: I think it would be reasonable for you to offer a paid service if folks wanted to utilize your support team for mod support, if your support team has the bandwidth to do that. If so, I'd say $120/hour is probably a reasonable rate. Not everyone would want to partake of the service at that price. But that's the point.