I wouldn't think so. The 12AT7 with a mu factor of 60 can be used as a replacement for a 12AX7 with a mu of 100. Probably too high for a 12AU7 with a mu factor of 19 though.
The tubes are electrically pretty similar, so you won't smoke anything, but as previous posters have noted the gains of the tubes are quite different, so there would be sonic change.
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