The lidp "osnap" will not cause AutoCAD to have a particular osnap active, but it will cause the result 'pt1' to be the point as if the osnap was active.
If you want just the 'endpoint' snap active when user selects, you could set the snap just before tht line, as in:
(setvar "osmode" 1);;or whatever endpt is
then you should restore osmode to original setting