Hi there!
You may edit the Solfege labels to use Sol instead of So and Si instead of Ti:
1. Open Little Musician
2. Go to the Media Library section
3. Click on the Solfege Labels tab
4. Click on the edit button at the bottom
We also do have a way of using the movable do system (in case this is something you are interested in) which you may access by following these short steps:
1. Open Little Musician
2. Go to the Tools section
3. On the left, click on Additional Settings
4. Click on the Solfege System dropdown and change it to Movable Do.
Kindly note that changing the settings to use Movable Do will only affect the note icons and note colors. They won't affect the voice recordings at all, so if you would like to use this setting, it is highly recommended that you replace the voice recordings with your own files.
I hope that this somehow helps!