Accounting implications of Membership Type changes

Under Administer > CiviMember > Membership Type, one can setup different Financial Types for different membership types. This can be used to have different financial accounts for revenue etc associated with different membership types. These choices are respected for front-end and back-end purchases.

There are also generally different costs associated with different membership types.

When renewals are done through the front-end or back-end, membership type changes result in appropriate financial type and amount for the associated payment contribution.

However, when a membership is manually edited and its membership type is changed, there is no automatic adjustment of any previously accepted payment or outstanding pay later amount still due. These changes can all be made by editing the relevant contribution associated with the membership.

Rather than trying to work out a business rule or rules to handle accounting in these cases of manual changes of membership type, I propose that we display the following message(s) when appropriate after the membership type has been successfully changed:
"The financial types associated with the old and new membership types are different. You may want to edit the contribution associated with this membership to adjust its financial type."
"The cost of the old and new membership types are different. You may want to edit the contribution associated with this membership to adjust its amount."