Never change the key ! For a very simple system , this is possible , but this is not bad practice, is a disaster. Add a priority column, if the table is over 10K rows put an index on the priority column.

In case you have to enter rows in between usually , there are options like :
- priority , real number
- 2 columns , priority and subpriority and reorder from time to time.
- priority as integer but with a gap in between like every priority multiplied with 100.

There is no very simple way to solve this :( .