If you only ever want to use one set of split points, the easiest (and best) way is to use Parameter Lock as Fred suggested!
This will prevent any registrations (or MIDIs) from changing the split points without needing to 'Freeze' the style group and remember to turn on Freeze. Remember that using Freeze obviously also prevents other parameters in the same registration group (Style) from changing, which you probably would want to change when you select the reg. so it may not be appropriate for you.
Using Parameter Lock, you can load and try out any registrations, either your own or third party ones, without fear of changing the split pints, however 'obscurely' the split points may be set if included in them!
You can still change the Split Points manually at any time, even if they are locked in Parameter Lock.
Once set, the Parameter Lock settings will remain in place until you change them, or you carry out a System Reset.
You should be able to stop regs. from changing the Chord Fingering Type too using Parameter Lock, assuming you want to do this.
Using a 'Start Up' reg. is great until you encounter a registration that has been memorised with different settings, however it does make it easy to 'recover', once you realise that they have been changed!
As I said initially, if you don't want any regs. to change your split point, use Parameter Lock. If you do want them to change for some registrations (maybe some of your own), then instead of using Parameter Lock, check the group in the Freeze group table and remember to turn on the Freeze button when you don't want them changed.
Why not try both ways and then decide which works best for you!
Regards
Ian