I had a load of files of the form _, where went from 1 up to 101. I wanted to rename it so started at 2, and wanted to use the sequential numbering feature, but this resulted in rename conflicts since it would try to rename filename_1 to filename_2 before it had renamed the existing filename_2 to filename_3 (and so on for all the files...).
While my suggestion in the title is to perform the rename in reverse order, this may not handle all cases (although I haven't really thought about the details TBH).
However it is done, it would be nice if DOpus was intelligent enough to detect this kind of conflict and handle it automatically.