First off which you can currently do - download all customer information in to csv.
The new process I am then suggesting is that:
When you need to update en mass, you can change within the CSV file all the details including customer setting like source type, sales type, email address, address etc etc - all customer fields.
This is then uploaded en mass linking the information to the customer unique reference and then overwriting the information in the current database.
This is obviously a process that has to have warnings all over it and extreme care needs to be taken when doing this however it would fine this extremely useful to do as last night i had to manually go through over 250 customer records and manually change their settings last night. It took hours and i was just changing Source type, sales type, email default.
This function is obviously not a day to day requirements but data requirements for reporting changes over time and database updates can be useful.
the finance system we use at work has this function but is only actioned by the support team at the software company. They charge a very small fee for doing so but it does save hours and hours of time and ensures accuracy so we are willing to pay for it.
Sorry I would not be able to convince work to use Kashflow, large global company with 600 employees. Though I do love Kashflow for our hockey club 400 odd membership. I've only used it for a year and about to roll in the colts section to it too.