GL Transaction Type - truncate description

I tried to modify transaction text and wonder how to truncate a text.
As mentioned in KB0106222 - Modifying Posting Engine Transaction Text, the GL Transaction Text (GLJrnDtl.Description) field is limited to 120 characters.
In my case I want to limit a part description to maximum of 20 characters, what is the way to do it?

I would offer to put the part information at the end so it truncates it for you. I don’t see a way to do string manipulation. Another option may be to use a UD field, but that would not be a great idea on PartTran…