The DataPump processes are stored in a SQL table that contains the path to the projects. You could try replacing all the D:\ with C:\ instances in a field in that table, using Monarch Pro.
Another approach would be to log on to the server using the service account for DataPump and to then run the subst command to map the letter D: to the root of drive C:\. I'm not in front of a server to try this so I offer it more in hope than expectation
For the projects, models, and batch scripts, I've found a handy trick. I do a windows search for .xprj, .bat, .xmod, ect in the folder for the Data Pump files. Then, I select them all, and open them in Notepad++ (free download). Notepad++ opens them all in one instance. You can then do a search and replace for D:\ to C:\ in all open documents. Finally close all.
I had given an estimate of 7 hours to my manager the last time we had a major change like this. I figured out the above trick in 15 minutes once I got started, and needless to say the boss was very pleased.