Even at the shala in Mysore nothing remains like 80 years ago. The changes are slow and slight, but they exist. I.e. nowadays only 2 paschimottanasanas are done (holding the toes and catching the wrist), in garbha pindasana students shall role only 5 times instead of 9 times. Urdhva dhanurasana is added, in the yoga mala this pose is not yet mentioned. Full vinyasas are not exercised, but only half vinyasas.
So far I've heard 2 reasons why it is good to stick to the tradition:
The series is perfectly designed.
There is the danger, that students never learn difficult asanas when they do free style, when they go too fast to the next asanas and omit those they are not able to do.
I see several reasons for adjusted series:
Sometimes we have not enough time to do the whole series.
Injuries force us sometimes to modify the sequence.
Ashtangis who practice 30 years or longer mention sometimes: boredem.
Yesterday the new book by Sweeney arrived. He has created several series. They look nice, but I don't think that I will learn them by heart and practice them. Beside the series many helpful hints are in the book, i.e. how to approach urdhva dhanurasna.
I am too lazy to learn new sequences so I prefer the flexible approach of Danny Paradise. The series is more or less the sceleton. Asanas can invite to do variations of it. Asanas can be added in order to deepen an asana of the series.
My variations, that I like:
Sometimes I do full vinyasas, sometimes half vinyasas or even vinyasas only after each pose.
I like to add asanas from time to time.
I like to do variations i.e. to bind, catch the wrists when doing parivritta parsva konasana, because I think that this deepens the wrist and this is a good preparation for pashasana.
It is good to finish here with: the guru is in you.