For Thomas More, the thing that makes the difference is what is called by others Lex orandi, lex credendi. I mentioned how he had, with Erasmus, mocked what he regarded then as the superstitious practices of the pilgrims at Canterbury. By the time he came to write the Dialogue Concerning Heresies, he had modified his opinion substantially.
These things (pilgrimages, veneration of relics) he considered in some sense to incarnate the faith and hold it together, like a tin can holds soup. They are not the soup, but the soup will spill out without the can. If you damage people's way of expressing the faith, then the faith itself will be endangered. He saw what that had done in Germany and he feared that if the English people clamouring for the same 'reforms' were to get their way there would be a lot more damage done not just to the external expressions of the faith, but to the faith itself.
A long time ago I wrote about how the faith in Ireland was damaged in exactly this way. When the expressions of the faith (Rosaries, pilgrimages to holy wells) were derided as being unliturgical, the soup began to spill out. Yes they were unliturgical, but they were not the soup, merely the necessary can.
If these things have been used for centuries to nourish and support faith, then one needs to be very sure what one is doing before getting rid of them. They may be mere externals, but then so are flying buttresses, and without flying buttresses, cathedrals fall down.
And yes, that does apply to the liturgy too. I'm just not sure what good can be served by scooping up the soup and trying put it back into a wrecked tin. What takes centuries to build can be destroyed in an afternoon.