Thanks Ed .
Gary , there is very little room on the lower barrel to play with but there are several modifications that can be made if you over cut the barrel . You can trim a little plastic off the end the refill but I always advise against that because when it comes time to change the refill the new one will have to be modified for the pen to operate properly .
You can use a Fisher Space pen refill without the plastic Parker adapter if you absolutely have to have a shorter barrel but the pen will only work with those refills , again I don't advise it .
If you trimmed the lower barrel too short by mistake you could add "Oops Bands" to lengthen the barrel . It would be best if you replaced the shortened tube with one of the right length but the flanges that press into the tubes on the hardware are long enough that you could carefully press them into the brass tubes even if the oops bands hang past the ends of the tube by a couple of thousandths , just don't press too hard or you could break the oops bands .
In the end , there are always ways to modify the cigar lower barrel to make them work properly , it all depends on what happened or what you are trying to do . If you need help , feel free to PM me and I will give you some alternatives .