How to combine mesh from Exodus2 file with data from CSV file

I have the following use case:

I would like to load the mesh from an Exodus2 file and combine it with data from a CSV file. The Exdous2 mesh contains cell regions recognized by the normal Exodus reader as blocks. Now the CSV file contains for different timesteps the values of a variable for each of the blocks.

# time,block1,block2,...
0,1,2,...
1,1,2,...
2,2,3,...
...

The value of a block/region given in the CSV file should be assigned to all cells within the corresponding block.

How would I approach this problem? Write a new reader? A programmable source/filter?

I have found this but how to do it for multiple time steps.

If implementing a new reader: Which of the existing readers could be an example? Do I have to/can I inherite from the existing Exodus reader?

Sorry, if this is already solved by some existing solution, but I have only found pieces of what I would like to do.