I use an updated torrent for updating files sometimes, but there are a couple files I don't want Tixati to update.
Even with a couple files unchecked (Off) Tixati still updates them..

So finally this time I set the files to read-only so that Tixati can't overwrite the files I have turned off.  Now I get this error instead: error, access denied.

Here's a screenshot showing that file is turned Off, but Tixati is still trying to write to it:

https://ibb.co/DkdHN9B

edit: also, when file error occurs, it stops the whole torrent instead of continuing with the other files it has successfully opened.

it may be that some of the files that are off overlap with files that are on, so in order to update the piece it has to wright to the off file.

i think you're right.  i had 2 tiny files off (and read-only due to previous frustration).  when i removed the read-only attribute to unblock Tixati, all the remaining 99% larger files resolved instantly.

this isn't a very intuitive outcome though is it?  as an end user i wouldn't expect a file set to 'Off' to be overwritten, i would expect those bytes to be dropped.  maybe to somebody intimate with the BT protocol that behavior makes sense, but it's not something i would expect.

Just rename is OK. Rename files on disk or those unchecked items in torrent.