Hi, welcome to LQ!
Code:
cat fortel
4506 PH443 WKLMOSFR31OHJKMCT02 ~|123456789
4506 FH3 WKLMOSFRABCHJKMCT02 ~|123456788
sed -r 's/^(.{27})/\1 /' fortel
4506 PH443 WKLMOSFR31 OHJKMCT02 ~|123456789
4506 FH3 WKLMOSFRAB CHJKMCT02 ~|123456788
If you're happy w/ the visual replace the 'sed -r' with
'sed -ri' to make the change in-file.
Cheers,
Tink