In a one-way dimmer, can C and L1 terminals be swapped?
The answer is swapping the line and load may cause problems depending on the electronics. Many dimmers use SCR's to control the output. These use a small voltage from the line side to turn on and off the scr at a very rapid rate. Some of the newer dimmers have more electronics and don't care which side the line is on but most do. Depending on the model it may work fine or not at all.  Note an SCR is a silicon controlled rectifier.