Hello Ranquin,
Cool! There is no one click mirror solution, but this little custom group on your Guide Curves object should do that for you (note: this node group should be placed above the Medusa Nodes Modifier:
But you will still have to paint the texture maps on the other side as well if you have any.
This is all this node group does:
Basically we can multiply the position by -1 on the X axis and join that to the original. Similarly how we would scale the regular object by -1 in the viewport to bring it to the other side.
You could also apply this node group if you would want to edit the mirrored guides further manually.