Both the LS-6i and the LS-5i locks can be re-keyed, but because they have different key-ways, they cannot be keyed alike. So 5i's can be keyed the same and 6i's can be the same, but a 5i and 6i combo is not possible.
- LS-6i: Schlage C6 keyway
- LS-5i: K5 Keyway (Kwikset)
The key blades and length are totally different. This is because they come from different factories. In this situation, typically a condo would adhere to a single lock model for all doors; ie. all 6i's.