First, now is not the right time to prune it. Late winter to early spring is best. The plant blooms on new wood, so you want to prune it while it's dormant.

When you say "long neglected" what do you mean? Is it multi-stemmed, or tree form?

Maybe it would better if you posted a picture or 2 for us to see, and we can make suggestions.

The stumps don't need to be treated in any way.

google the name ROS .. then hit the IMAGES button ... i have to bet there are thousands of pix online .....

when you are ready ....

start at the bottom.. and limb it up as far as you need ...

then look to the interior and remove all crossing branches ...

then put down he shears for this year.. and observe the plant next year ... no one said this has to be done in one year... or one cutting session ...

if you have more than one.. do one.. and inspect the results next year ...

what stump pieces ...??? at ground level??? if so .. consider its natural shape.. and try not to force it into your preconceived notion .... in other words.. if it is multi-trunked... leave it that way ... if you want a single leader .. consider removing the whole tree ... as you suspect.. leaving stumps, in the long run, is not healthy for the plant.. though i doubt you could kill a ROS ....

if you mean stumps from where you are going to prune.. up in the tree ... please research proper pruning techniques ... as you should NOT be leaving stumps in the tree

good luck

ken

I prune my ROS every other year late winter. I cut all the branches back to about 2'-3', attempting to keep the shape oval-ish close to its natural form. I may thin it a bit removing wayward branches from the base.

Now Ken's limb'ing it up approach is not something I've heard of for ROS before. Maybe that's more of a "tree" style. I'm thinking more along the lines of shrub near-rejuvenation.

I guess we need to see where you are starting from. If it is already a tree, maybe its too late to be a shrub???

Here's mine at about 5-6' after being cut down to about 3' late winter. Full of bursting buds that the JB's are getting ready to pounce on LOL!

{{gwi:269762}}

These are very tough plants and you can pretty well have them in any shape you want. I admire those pruned to a single stem and then allowed to branch like a tree but mine was planted to cover a fence and I've let it branch from the base and get just as high as it wants. I cut back some branches this spring that were leaning out into the path and just this past week I trimmed a few back that were weighted down by soggy blooms and barring access to a gate. It's covered with flowers (large, single white with red throat) and is putting on a great show.
The best time to prune any shrub is immediately after it flowers - that way you can be sure you're not trimming off next year's buds. But if you are going to prune out a main stem, take it right down to the ground without leaving a stump. And if you tip back side branches, cut back to a side shoot so it will branch out and not die back.