- In Excel
- File > Options (Figure 1) > Proofing > 'Custom Dictionaries'
- Select the dictionary you'd like to add the word to (Figure 2)
- Click 'Edit word list'
- enter 'HSA' in the word field
- Click 'Add'
- Click 'Ok'
- In Excel
- File > Options (Figure 1) > Proofing > 'AutoCorrect Options'
- Type the word you are trying to type (HSA for me) in the 'Replace' field
- Look for the replace/with combination you are hitting (HSA/HAS for me)
- Highlight the record, click 'Delete', then click 'Ok'

Figure 1

Figure 2
Figure 3