I have a part that's been created in an ass'y (have not made as external part in that it is not needed as such).  I'd like to mirror it to create identical across a plane.  I cannot do it as a part (mirror) in the assy.  I thought maybe I can pattern/mirror at same time?  Or is my only option to make as external part then save as a new part and flip it, bring in as a new component to assy?  Btw, it's created from (mainly) a spline so not on flat plane, not sure if this is part of problem?

it is the yellow that I want to mirror (showing spline in 2nd pic)

thanks,

b