Did Chessie System locos pull CSX coal units?

There were still Chessie painted locomotives on CSX's roster in the early '90s.

You are correct in removing the C&O reporting marks, or B&O and WM for that matter, and replacing them with CSXT. You would also have to renumber the engines per CSX's model designations.

There were dozens of Chessie-painted units on CSX in 1992. Most were of EMD manufacture (9 different models), but just a handful of GE engines (1 U23B, a few B-30-7s). Not all of these had their reporting marks changed yet, as my photos at Brunswick,MD. show a few units unchanged thru the mid-1990s.
By the end of 1998, only 28 Chessie units remained (GP38, GP40)
In 2002, only 4 GP40s remained in the Chessie colors.

Ditto what others have told you. I went to work at CSX in 1991 and not only did we have lots of Chessie painted equipment we still had units in their Pre-Chessie paint - B&O/C&O "blue dip", WM Red-white-black, grey Seaboard, SCL and on and on. The creation of CSX swelled the ranks and it takes a long time to get around to repainting every unit. Yes, reporting marks all changed to "CSXT" usually with a simple stencil.

To illustrate...

I will not change the reporting marks or numbers....but these will run together time to time.....

yes, it would be accurate, and you do not have to reletter (unless you want to)

Here are 2 photos of Chessie engines retaining their reporting marks well into CSX.
Photo 1 is a GP-40-2 leading the daily Hanover,PA.-Hagerstown,MD. turn into Hagerstown in March,1998.
Photo 2 is a wb  Chessie empty coal train rolling through Bailey's Wye in Baltimore,MD; NOTE Orioles Park at Camden Yards in left background, and concrete abutment of just removed road overpass behind engines. 1993 photo.

Here's a B&O unit trapped between 3 CSX units taken in Collier Yard Petersburg Va.: