Why these threads seem to take on such a polarizing vibe is puzzling to me.
It's a weird issue. It's on the borderline between a basic and advanced thing to do. On classic amps changing the to a new type and rebiasing or modding to support them is definitely something a qualified tech would be involved in, and is deep in the realm of "off the beaten track mods".
But at some point amp makers like Mesa Boogie starting doing A) fixed biases, B) tubes tested to match that bias, and C) 6L6/El34 switches. This made it pretty user serviceable to swap tube types. So it's a complicated change that was given a simple button thanks to a lot of engineering and business work on the companies side.
And there's a lot of mystique to people taking Marshalls and modding them to kt88s, etc.
Lots of people don't want to have to understand things at an amp tech levels, they just want to have one button that says "mod my amp to kt88s and tell me how it sounds", or "let me do the same thing I did with my dual rectifier when I flipped it to EL34".
But the flip side is that the real amp tech that modded that Marshall to KT88s probably did a handful of things to make it play nicely and sound good, maybe even did a transformer swap.
The other group seems to be people that have read and understood what the different aspects are of doing a swap and presumably come to the conclusion that "It can be done already and you just need to learn how".
So from Cliff's side I see three main things:
a) adjusting those things is all already possible, with finer control than people are asking for. Like replacing the Depth Mode switch on Bogners with a depth control.
b) How would you even automatically make the change for all amps? Some amps (like Mesas) have a standard configuration for both 6L6s and EL34s, but what's the "standard configuration" for a '59 Bassman with EL84s? A real amp would need a transformer swap, and now the transformer match parameter depends on what was used. If an ideal match was used... it would be 1.0 like the Axe uses already. Doing math to pretend you didn't do a transformer swap wouldn't be any more "Authentic" than what it currently does since in real life that wouldn't be possible.
c) There's a lot of numbers and math involved in figuring out the transformer and power tube interactions. Specs of the transformer, specs of that particular power tube, and the fact that tubes had variance so sometimes they would be more or less of a match despite being biased (which could also be hotter or colder). My assumption is that a lot of those numbers don't actually have to make it to the model because in terms of simulating the effects all that stuff just boils down to "What's the Transformer match ratio?". So the current behavior isn't "Cliff is doing a bunch of changes I don't want behind the scenes to make the transformer match the new tubes", it's "I'm only changing the tube type so only the tube type changes". To set up this automatic calculation would involve adding a bunch of values to the different tube types, and a bunch of values to each model to use for calculation.
That, and I don't know if there's anything currently in the Axe FX where changing one value makes other values change for you (short of block type). Implementing this adds a whole class of UI functionality and bugs for both Axe Edit and the devices themselves, And confusion when you tweak one value and then tweaking another changes the first. Or a new UI paradigm where you can enable or disable the linking, and confuse users who haven't learned that yet.
I think where I've ended up on this issue is despite understanding how "nice it would be", practically I don't see how it could be done in a good way. It seems like the best answer is either a tech note or manual section explaining the process instead of a function in the code that does it for you. A calculator to give you a starting point also sounds nice, if you want to know the "authentic" value before tweaking.
But I think even that's a bit of a flawed concept: Some amps have a tube type switch that really do have an authentic value for those two types. But most amps the authentic value depended a lot on how the amp was modified to use a completely different tube type, so just using a calculator is really just answering the theoretical "what if I could somehow put this tube into an amp without changing anything else to make it work", where the Axe FX works like "What if this power amp was designed for this new tube type instead".