Consequences of rooting HTC One X? All I want to be able to do on my device is to be able to use Titanium Backup.

I don't want to install custom roms, I want to keep everything as-is but be able to run apps that need root like the above.

If I do root my device, will that stop OTA updates from installing? If they do install, will it need re-rooting again?

Can devices be un-rooted?
Yes, most manufacturers (AFAIK including HTC, as I had this experience with my EVO 4G) will have the OTA update break if the device is rooted. This may have changed, but to my knowledge, OTA will not work after root.

However, devices can be unrooted, however, some are easier than others, and the process is different for most devices. Please note that most unrooting methods require a full wipe. Thus is the nature. 

However, if I can give you a bit of personal advice, custom ROMs can usually give you the features of an OTA update and much, much more ;)