Many times the saddle sit bone break-in points will be identical to your already required position.

The ability of the leather to learn a new break in point will be determined first by the present condition of the used saddle surface. If surface is smooth and only dimpled to the previous sit bones, you may find it practical to ride the saddle and the you find the points will shift to the new sit bones. A little, very little tension may be required.

If the leather is has surface cracks, (from drying), additional care and treatment may be required.

I have read several suggestions on this forum, but never found the need to try. I have had no issues with two saddles, a Brooks B15 that was already fitted to a 1973 model road bike, and a Brooks B17 purchased used and barely broke in, almost new really. I measured the dimples on these saddles and found them almost identical to those on a B17 Imperial that I broke in from new.