Just because games use the Steam Workshop for modding doesn't mean mods can only be added via Workshop. In fact, many games that use Workshop can be modded with files downloaded from other websites. Two good examples are Garry's Mod and the Source Filmmaker. Both programs have a lively modding community that does not put their content on the Steam Workshop.
Are there any plans to get KSP supported by the Curse Client or (preferably) Steam Workshop? I've tried using community-developed mod managers, but they haven't worked out for me. Now the game goes Challenger whenever I try to launch it. What I need is a simple mod manager. I'd like to be able to add, remove, enable, and disable mods on the fly, much like games using the Steam Workshop.