If you use G6 mode 31758/21667, see if that gets the combo you want. (I did. I used PKHeX to get that combo)
Hmm, I also see it's difficult changing the text in G7 mode, I'll have to change that up.
edit: I fixed it, since it is a bug that is rather important.
Should be fixed in ver 1.0.5
edit again: made ver 1.0.6, to stop any program crashes due to user inputting invalid/impossible combinations, as well as patching a bug regarding setting both to 65535.
Gen 6 mode TID/SID max value is 65535/65535;
Gen 7 TID max is 999999, but doesn't work with max SID (it seems max for 999999 combo is 4293). By itself, SID max is 4294.
[remember, both modes are derived from the full data of max 0xFFFFFFFF]
Here's an example of how it looks like