They are not what I would call responsive. From grabbers I used in the past I remember they had this feature, which is why perhaps you would consider it as well
Unless the change is something to do with Daylight Saving starting and/or finishing, I suggest you find an XMLTV post-processor to correct the data before importing into MC. There are lots of XMLTV processing applications around. There is bound to be one that can import an XMLTV file, make an adjustment, then export the result.
For XMLTV MC just runs an external process, then imports the result. There is no logical place to put time adjustment function in that work flow.
The other thing you might look at is your location settings, compared to the source. Maybe something changed there, resulting in you accidently shifting time zones.