How to shift one channel's programs by an hour

Dear list,

The source of one of the grabbers I use provides incorrect information
for one of the channels that are of interest to me, in that all programs
are listed as starting an hour earlier than they actually do.

Obviously this needs to be corrected at source, but since I have no
influence over that I would like (at least temporarily) to postprocess
the xmltv file to shift the time stamps for this particular channel by
an hour, leaving all other channels in the file alone.

Do you have any recommendations for how to achieve that?

Many thanks, Jan