If you're increasing the working temperature, read through the design requirements of API-650 Annex M carefully. Many tanks which satisfy the basic standard won't meet the Annex M requirements.
I assume this would be a change-of-service under API-653.
You may need to check for increased specific gravity. Corrosion may be more of an issue. If insulation is required, you have considerations with insulation supports, personnel access, roof loading, etc.