Aaaa...I won't really say that ;-). VentureCraft & I had a very long conversation (probably would have been shorter if it weren't for the alcohol involved) about this - especially when they were offering promo spare tubes for the TT. So the official line is that OpAmps and tubes are meant to be replaced by the maker only. They're not completely rigid about that but they always have that warranty guideline to fall back on should they choose to exercise it.
Edit: This is one of the reasons why Musica Acoustics has this huge disclaimer in their TT page. I helped them proof read and correct that.
Thanks Anakchan for correcting me. It's true that you need proper knowledge/equipment to switch those part. I almost broke MUSES02 pin, when first swapping it on my LE.