[Mesorah] S. Baer on Shelo Assani Nochri

[R. Rich Wolpoe]

«Very much so.  If you're not washing from a natla then what you are
doing is not netila, so how can you say "al netilas yodayim"»

Rashba disagrees. He thinks the b'rachah remains unchanged

Another alternative to Rosh's newly coined B'rachah is to recite no b'rachah at all, EG as many do for washing for davar shetibbulo b'mashqin.

I haven't see the Rosh in a while but this debate is brought down in the AhS and he seems to favor Rashba but is resigned to Rosh and Tur due to either their status or the widespread acceptance thereof.

Which means that the AhS at least at times was willing to leave a problematic nusach as is. 

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Which also raises the issue -

Nani'ach that a bona fide Gadol proposes a change. Does the Pre-existing Minhag [before the change] serve as a valid source for resisting that change?
Shalom and Regards, RRW