OK so I downloaded a rather large torrent, and Tixati started to initialize the files. When I checked though I only have 200Gb free, so it's going to fail anyway.

Is there any way to get Tixati to start but not carry on initializing these files? Like remove the torrent somehow or change the settings (registry?) so that it no longer pre-allocates?

Currently when I start it the hard drive is working flat out and the GUI isn't drawing, as though it's too busy doing the initializing.

Any help appreciated!

Do you have it set to not show the pre-download confirmation window?  Because you can uncheck files in there, before allocation happens.

Go into Settings > User Interface > Behavior, and next to "Transfer loading priority/location prompt" click the configure button.  Make sure you have the first two in Contexts checked on.  And the four in Conditions all checked on.  This is the default for new installations.

If it already initializing and you are past confirmation, press stop and then go into files tab and uncheck files you do not want.

use sparse files by default and it shouldn't be a problem