Hello
When we change a sketch of a reference plane, and it has symmetry relations with a plane of symmetry (frontal), this relationship is lost, of course, so a missing reference but how to edit the plane of symmetry? to define a new one.
You can edit the repetition relationship but not the symmetry... or I can't find how.
This forces me to delete all the mirrored entities and recreate all the symmetries.
So when I can, I cheat with repetitions instead but it's not great.
Dear @Sylk
If you only make your symmetries in relation to shots, it works.
If you systematically make a plane that is dimensioned in relation to something (a plane other than the front, side, bottom planes for example) Then if you change the dimension of plane 2 your symmetry changes.
You should give a mini example so that we can be sure to answer you correctly.
To pluche
Hello
I agree with zozo_mp, for my part I always create an originally-linked plan for my symmetries (habit to get into). So no unpleasant surprises.
Hello
As a simple example, a circle sketch drawn on the front plane, a symmetrical circle with a top plane as the plane of symmetry.
If I change the sketch plane from front to top plane (to reorient the direction of creation of the part), the plane of symmetry is lost and so I try to edit the relationship to assign the face plane as the plane of symmetry.
Symmetry is preserved as long as the entities are in their proper place, except that it creates a slew of wobbly relationships.
before:
after:
Hello, if you don't do a symmetry via a construction line I guess there's a good reason, but I've never used a symmetry in a sketch via a plane, I've always used an internal sketch path, and since the path follows the plane change, no worries.
Yes, Hello, @romain_becdelievre certainly you don't have the wobbly relationships anymore but you can't change the axis of symmetry either 
Since we can edit the circular repetition relationship to change the center, I find it weird not to be able to edit the plane or the line of symmetry...
I didn't understand that you were going from a front shot to a top shot.
It seems normal to me that it does not work. Because it calls into question all the norms and practices seen above, seen from the left, etc...
Hello @Sylk ,
In a plane sketch, symmetry with respect to plane only works if the plane of symmetry is perpendicular to the plane of the sketch, the selection of an " oblique " plane is impossible.
SolidWorks is in fact symmetry with respect to the intersection line of the two orthogonal planes.
If the sketch plane is changed, but it remains perpendicular to the plane of symmetry, the symmetry feature in the sketch is preserved. Otherwise, the sketch is in error...
In the case of a plane sketch, selecting a construction line as the axis of symmetry seems more appropriate.
To modify symmetry, a construction line dedicated exclusively to it can be used as an axis of symmetry.
It is then sufficient to modify the construction line to act on the symmetry.
Kind regards.
Hi @Sylk
The solution seems to me as simple as creating a plan that coincides with your basic plan.
If you change your orientations, you can always modify your " plan " function to reorient it as you wish. Your constraint in the sketch will follow as it should once the plane is reoriented so as not to generate an error.
On the left the symmetry related to the plane named ' plane of symmetry ': not the error following the reorientation (and modification of the definition of the plane), on the right what you usually did with the error on the impossible to repair symmetry.
To answer the basic question, it is possible to redirect the constraint.
Bear with me, this is my first capture gif
Hello Thank you all for your answers.
Indeed, I totally agree with the basic best practices and the use of lines, but some cases require a redesign to get back on track. By avoiding as much as possible a retake from the beginning, where a simple edition is enough.
Thank you @stefbeno this is exactly what I was 
looking for 
PS: and your GIF is perfect!
And ideally, to get back on track in the process, add the symmetry line and redirect the relationship before changing the sketch plan.
