make a copy of the torrent files to be on the safe side.
then, stop the torrent
if you have set to , select the torrent from the transfers list then click the tab on the lower panel.
Under , click the button and point it to where your finished file is located.
Then click the button. If it matches your files to the torrent metadata file, 100%, then simply restart the torrent.
This is a very frequent task for me, but for a different reason. Lets just call it replacing a file safely. Turn off the torrent. R click open folder/ chose file/rename and copy the file name. Now add a 1 to the beginning or add a .bak to the end. Now go to the directory with the file you want the torrent to use, copy it to the directory the original file was in. Choose it/ rename and paste.
Do all of this in explorer. Now go back to tixati and force check then restart. You can just restart because tix does an auto check on start up of any torrent. Don't be surprised if you are 99% just let the file complete.
Now go back and clean out the other copies of the file.
You can do this with partially completed torrents. Thanks to retaggers there are many copies of the same file in different torrents. If you have a stalled torrent at 60% you can copy the file to another stalled torrent at 60% and possibly complete the file.
Things are weird when you do this, depends on the file structure and how big pieces are and which file was where in the torrent, but you will likely recover a large % of the data for the second from the first. That is why it is so important to never let files get copied over, you must keep every copy because sometimes you don't recover enough data and need to find a third forth or fifth torrent to try.