Yes.

If its an RTF, the easy way is to bend the steel rod until the wings are flat, then make appropriate balsa wedges & glue them into place -- use Probond or epoxy.

The proper way is to cut into the end ribs & glue in a suitable ply wing joiner behind the leading edge spar, behind the main spar & at the trailing edge spar. Then make wedges & glue them in. This is a lot of work, but it is a fair bit lighter.

If it's an ARF, without the steel rod, the second method is the only choice. The Superstar is particularly responsive to that mod, especially if you have enough power to make life exciting.

If you are going to flatten the wing, you should also lower the wing 3/4" into the cabin & trim the rear of the cabin to fair into the rear fuse. This mod is well worth the effort.