Short answer: yes, and it is normal practice — but only at the end that does not do any work, and never on the diameter.
What "60 HRC" on a pin actually means
A nitrided SKD61 (H13) ejector pin is not 60 HRC all the way through. It is roughly 60±2 HRC at the surface and 42±2 HRC in the core. That is deliberate, not a compromise.
A pin hardened to 60 HRC through its whole section resists wear beautifully and then snaps, because there is nothing ductile left to absorb a side load. A pin at 42 HRC throughout survives the side load and galls in the hole. You want both, so the hard case goes where the rubbing happens and the core stays tough enough to bend a little instead of breaking.
The case is thin. That is the whole point of the next three paragraphs.
Cutting to length
Cutting removes the case at the cut face and exposes core material, which is around 42 HRC — tough, but not wear resistant.
Usually fine: shortening the head end, or trimming a pin that stands proud, where the cut face does not run in a bushing or against a moving surface.
Not fine: cutting a pin so that the new cut end becomes the working end running in a guide hole. You have just created a soft wear point at the exact place the pin is loaded, and it will wear a bell mouth into the hole faster than the pin itself fails.
Regrinding the diameter
Do not. Grinding the diameter removes the case over the whole working length, and once it is gone it is gone. The pin looks correct, measures correct, and lasts a fraction of its life. This is the most expensive way to save a pin.
If a pin is worn on diameter, replace it. The pin is cheaper than the downtime.
What to do instead
Buy the length you need. Standard catalogue lengths exist because they cover most cases, not because they cover yours — and a pin made to your length keeps the case where it belongs on both ends.
This is the real argument for buying non-standard lengths rather than buying long and shortening: not convenience, but keeping the treated surface intact where the part does its work.
One counterintuitive thing about the price
Ejector pin cost does not track steel mass the way you would expect. From real per-specification supplier data, a Ø1 × 200 mm pin costs more than a Ø3 × 150 mm one — less steel, higher price. The reason is grinding, not material: a thin long pin deflects under the wheel, is hard to hold straight, and scraps more often. You are paying for the attempts, not the steel.
Practical consequence: if a pin position on your layout has any freedom in it, going one diameter up can reduce your cost rather than raise it. A catalogue price list sorted by size makes the cost curve look linear. It is not.