No need for acrobatics, just call command & draw the polyline:
(command "_.PLINE")
(while (=(logand(getvar "CMDACTIVE")1)1)
(command pause)
)
;;once command returns, you can get the entity association list of the
last entity,
(setq elist (entget(entlast)))
;;and modify it to your liking.
If you prefer, you can get the list of points and create the entity
without calling command, using either Active X or (entmake).
By "change the polyline into a revcloud," I am assuming you want to do
something like 1) check the length of pline segments 2) add/delete
vertices if necessary to control the length of segments 3) check the
direction of the pline to see which side is "outside" 4) add a bulge
factor to each segment to get the "cloud" effect.
If you have ACAD2004, the ability to "cloudify" an existing pline thus
is included in the Autodesk supplied REVCLOUD routine.
Even so, you could do it for the programming exercise, if you feel like
it.:)