If i do this:
c:\adb>fastboot boot twrp.img
cannot load 'twrp.img': No such file or directory
and after one .img delete:
c:\adb>fastboot boot twrp.img.img
downloading 'boot.img'...
OKAY [ 2.800s]
booting...
OKAY [ 0.230s]
finished. total time: 3.031s
And coming the old twrp, not the new