...escorting three DFW's with four other Albatrosses behind me. As we neared the bombers' target their lead and #3 broke off to the north, while their #2 continued on his course. I gave it a minute or so to see if 1 & 2 would return or if 3 would eventually join them. When it became evident that neither of those was going to happen I ordered "split" and the rest of my flight went off in search of the wayward DFW's while I followed #2.

Not long after that we arrived over the target airfield and I heard the aircraft I was covering drop his bombs. Then he broke away and joined up with his leader and #3, who were being dutifully protected by my four squad mates, Leutnant Bohme having replaced me in command. We all circled back around over the target and then the bombers went home.

Here's my question. Is there a way for me to retake the lead position after relinquishing it like that?

no, not that I know of. Plus since you split, my experience has been that any air victories you now make will not be counted as you now have no witnesses.

I would dispute the claim about the erm ... claims. You can still be credited with a victory even if there are no witnesses.
As to the split command, you are informing the rest of your flight that you are the one separating from the rest of them and that they should not be following you. I don’t think there is a way to reverse that order.