Hi Stephen,
If the valve stem has split, then it's an easy job for a tyre shop to fix. They need to take the tyre off the rim, rip out the valve stem, fit a new stem, and refit the tyre.
Don't ever fit a tube to a tubeless tyre. Not a good idea.
Tip: Check the DOT code on the tyre - there should be the word DOT followed by 17 or 18 characters and you need to look at the last group of 3 or 4 digits.
If it's 4 digits then the tyre is newer than 2000 - it should say something like 2204 where 04 is the year and 22 is the week number that the tyre was made.
If 3 digits, like 229 which is week 22 of 1999 - then it's time to say goodbye to the tyre. Even if the tread is new.
Robert