I know you are involved in, if not spearheading, a project to identify the burial sites of Mississippi veterans. I have one name to add to your list, that of Moses Pearson, who transferred from A/Hampton Legion Mounted Infantry to the 18 MISS in Nov 1864 in exchange for William Eggleston. I assume that Pearson went to Company K, that being Eggleston's Mississippi company. What makes this exchange unique was that I can find no connection of Eggleston to South Carolina, nor of Pearson to Mississippi -- no identifiable relatives of Eggleston in the Legion, and I assume none of Pearson in the 18 MISS.
I am showing a date of death for Pearson of 5 Apr 1865. His family genealogy website states he was mortally wounded at Fredericksburg, but I discount that, since there was no fighting at Fredericksburg at that time. i assume he was mortally wounded in the final assaults at Petersburg; that would also correspond with Sailor's Creek.
A cenotaph is located in Oak Ridge Cemetery, Bennettsville, Marlboro County, S.C., which only gives the year of birth and year of death (1823-1865); his family genealogy web-site gives a date of birth of 4 Jan 1823, in addition to the date of death given above. At any rate, you can add the cenotaph to your list of Mississippi burials. His family was moderately prominent in Marlboro District.
I suspect that the transfer was the inability of Pearson to be able to provide a mount; the vast majority of transfers late in the war were for that reason, in exchange for men who could provide one. But I cannot discover any connection between the 18 MISS and the Hampton Legion; they were fighting at different places, had not been brigaded together, or even been in the same division at any point in the war.
Moses Pearson initially enlisted in L/20 S.C. at Bennettsville on 3 Apr 62; he was on furlough in Aug 62, then was detailed as a teamster from Sep-Dec 62; he transferred to Capt. Peterkin's Cavalry Company, which was assigned as N/20 S.C., on 1 Sep 63 (this was an independent cavalry company raised form Marlboro District). In the spring of 1864 Capt. Peterkin's company was dissolved, and the men assigned to infantry units, except those who could provide a mount, and were willing to go to active service in Virginia (the 20 S.C. had been in a relatively inactive role north of Charleston), and those men were assigned to the Hampton Legion Mounted Infantry, then outfitting in Columbia (after converting from infantry). Pearson is shown as present on the Sep-Oct 64 roll of Comapny A (the first existant roll for 1864), and then shown as transferred to the 18 Miss on the Nov-Dec 64 roll.