I would start by appending the files to get one big file. That is the Append task in EGuide. Then SORT by Customer and date.
Next, you will have to write some SAS code to transform the 12 (say) records per customer into 11 change records; that uses the LAG function.
If you are looking for one value per customer (rather than one per month change), you could do that in an EGuide Query using the MIN and MAX aggregate functions. If you use the Query Builder, you can skip the SORT. (Your question is not sufficiently specific to tell what you want.)
The plots could be as simple as bar charts (poor paper-to-ink ratio) to a tile plot or a series of maps.