Possible to change single sided property of line during play?

[ExplosiveRunes]

Is it possible to alter the single sided/double sided property of a line in any way during play, or is that unalterable once its been defined by the map?

[Empyre]

In order for a line to be double-sided, there has to be a sector on the other side of the line, and vice versa. You cannot insert or delete sectors while the game is running. I'm afraid the closest you can get is Line_SetBlocking. If you also use SetLineTexture, you can make it look solid or not solid.

[Linguica]

It's unclear what you're asking. Do you mean you want to change a line from single-sided to double-sided, or do you want to change some other property of a linedef, like the tag / action / texture?

[ExplosiveRunes]

Just change it from single-sided to double-sided, or double sided to single sided, using ACS or otherwise.