https://www.youtube.com/watch?v=XOwR89pA_e8
This should help. Didn't watch it myself... The key thing is to make the length a custom parameter in the ipart table (right click on the column)
Use iLogic Copy? Please consider voting for this long overdue idea (not mine):https://forums.autodesk.com/t5/inventor-ideas/string-replace-for-ilogic-design-copy/idi-p/3821399
