fields:
I am guessing that you are using a symbolic type line (a screen shot would help) that has a pattern, and you want to switch the end of the line where the pattern starts. You could mirror the line, perpendicular to its direction, on its midpoint.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David