What's the drop out spacing of your frame?
If a 5 speed, there's a STRONG chance it's only 120mm.
9 speed "road" will be 130mm.
You can spring them a few mm, but 10mm is too much, without some bending of the faces to keep them from exerting a bind on the cones. (I feel I may have been "eating" DS cones on a couple bikes that I got a little "aggressive" in spreading by jamming a wheel in.
At that point, you may as well to a "proper" cold setting".