Add>Line, Options: Board Geometry / Outline, Line Lock set to "Off" for any angle, 90 or 45 are possible, also Arc can be used instead of Line for arcs.
Add>Line, Options: Board Geometry / Outline, type x<space><XLoc><space><yLoc><enter> at the Command line for each point, you can also use the incremental "picks", ix<space><xInc><enter> and iy<space><yInc><enter> if you prefer increments. Like:
x 0 0
and so on, you will need to add points until the outline is completed in one go. Entering co-ordinates won't care about the line lock.
You could display only the outline and Export a DXF from that and then Import the DXF to another BRD file. You could copy and rename the BRD file in Windows Explorer and load the Logic into it - in 16.6 one BRD file can be a template for another design.