I have never used a room temp. lye mixture but I know I read it once online that you can do that. I myself would warm it to what your recipe calls for.
It all depends on the type of oils you are using. I use room temp lye when I'm making soaps with oils that require no melting beforehand, like 100% Castile soaps or, 100% coconut oil soaps.
I like my lye warmer for all my other soaps. If it cools off too much before I use it, I do what pinkduchon does- I set my lye/water container in a bowl of hot water to bring the temp up, and I continuously refresh the hot water as needed until the desired warmness is reached.
I like my lye to be cool. Sometimes I stick it in the fridge, but it's never warmer than room temp.
I mix my oils in 35lb pails. Then scoop out a 4 lb and store them in glad plastic containers. So when I'm ready to make a batch the hard and soft oils are already mixed. No need to heat the oils either.
This info is great.. yet another sign that I only know a fraction of all there is to know.. I always had a stressful ten minutes or so with a sinkful of ice trying to get the oil to cool down before the lye gets too low. It never occured to me that you could warm it back up.