Ability to change the membership fee in bulk

[wmortada]

There is already a ticket about the ability to change the subscription amount for an individual contact (see issue #6) and work has been done to implement this in version 1.9. However, I think it would be good to raise this as a separate issue as it is a significantly different use case and I think it would be helpful for other membership organisations to be aware of this limitation.

The use case for #6 is that an individual supporter who would like to increase/decrease their regular donation. This is simpler because it is only dealing with one contact/customer at a time.

The use case for a membership organisation is that they would like to increase/decrease the membership fee for all of their members (or all of a type of membership) at the same time.

For example, an organisation has their membership set up as follows:

• Standard £20 (10,000 members)
• Student £10 (2,000 members)
• Organisation £100 (1,000 members)

Payments are taken annually.

Say the organisation wants to increase the membership fee by 10% for standard members. This increase would apply to all 10,000 standard members. Let's say 30% of standard members pay by GoCardless. This means we would need to increase the GoCardless subscription amount for those 3,000 members. This would be a pain to do manually so we'd need some way to automate this.

See previous discussion about this topic in #6.