Most ILS approaches include localizer minimums that can be used if the glideslope transmitter or receiver fails. For example:
In this case, to fly the ILS you would intercept the glideslope just before PRAIZ and fly the 3 degree glideslope down to minimums.
If we were cleared for the ILS approach, but we instead wanted to ignore the glideslope and fly the LOC only approach1 (for whatever reason: training, practice, etc.), could we do that without specific ATC approval since it is on the same chart and says "ILS or LOC"?
1 We could fly the LOC only approach by crossing PRAIZ at 2,200 ft. and then descend at an "optimum" rate until leveling off at the MDA of 520 ft.