Thanks everyone for the feedback.

First of all: this is not an automated edit, I made each change manually and did not use any script or even "search and replace". I did filter planet.osm to find the nodes with issues, but edited them one by one and steered clear of any that could be problematic (elevation in feet, approximations, comments and names in languages I did not understand, etc.). There are still 274 nodes with non-numeric elevations.

I was also not aware of a limitation of size for the area covered by a changeset. What would have been the correct way of doing this? I will keep it in mind if I do another edit of the same nature.