How to change the axis that mirrored parts swivel on?

[HeyThisIsntFallout]

So, i'm trying to build a craft and this problem arises every so often; I am wondering how to change the focal point of mirrored parts. Here's a shot because the few threads where I think this is the problem people are asking about, there is always a confusion on the interpretation of the question. 

The current mirrored rotation of these lights means they rotate with the small yellow arrows and "meet" on the yellow axis/arrow. I want the lights to meet and rotate outward from the blue arrow so that, if the blue arrow (by the VAB door) is 12 o' clock at this angle, the lights are sitting at like 2 & 10 (as opposed to 2 & 4, right now). Essentially, rotating the mirror focal point 90 degrees.

Let this jankily drawn representation be the standard by which all understand this dilemma and hopefully find their answer.

[Dafni]

I think I get what you meant. My trick is to build in the SPH and rotate the whole craft, sometimes the symmetry axis or focal point will change. Altought I can never say wich way will work, I have to rotate the whole craft around and try. It does not always follow a strict logic I think, or at least none that is obvious. Sometimes even changing the root part can flip symmetry axes around.

Dont know if this helps your craft, but its definitely worth a try.

[FullMetalMachinist]

I'm pretty sure that the mirror axis is tied to the coordinate system for the VAB, and there's no easy way to change it. 

One way to work around it would be to take off your cargo bay, rotate it using q or e, and then place it. Then place your mirror parts, then take off the cargo bay, reset the rotation using space bar, and then put it back on. 

(disclaimer: it's been a while since I've had to do this for myself, so it might not work, not 100% sure)