JDE standard depreciation methods vs User created depreciation methods

When creating a new depreciation rule which has been copied from an existing standard JD Edwards rule such as '01 Straight Line, Remaining Life R, 240 periods' and creating say 'Straight Line, Remaining Life, 245 periods', should the depreciation method still be '01' or do I need to create a new depreciation method code which has an 'Alpha Identifier' such as 'C1' and attach my new rule to 'C1'?

If I don't use an Alpha Identifier in the above example are there any implication if we upgrade, that is would we lose this new rule, any other issues?

If I don't need to use an Alpha Identifier because my new rule is using the same 'methodology' as the standard JD Edwards rule (same rule conventions, same formulas only say a change in extending the life from 21 years to say 22 years), when should we use Alpha Identifiers?  Only when the Depreciation Formulas do not follow that of the existing rules that is methods 00 to 18?  That is, when should a new rule not be set up as say '01' but have an Alpha Identifier?