Change the current .csv export for a table

Hello! Right now we a .csv export function on a button that sends all the data (all rows, all entries) to a csv export. We want to change that, so that custom data will be send and for selected fields only. This will require to implement a checkbox in the table, so that the client can select what entries wants to export. The following informations needs to be added to the .csv export file: A column - the total amount of the order - db B column - client code - something hardcoded (I think) C column - full name of the client - first + last name - db D column - full address - db E column - city - db F column - postal code - db G column - country - hardcoded H column - contact name (same as 3rd field) - db I column - e-mail address - I don't know yet, possible empty J column - empty ?! K column - total amount of pieces L column - content: I don't know yet M column - weight: 1 always (I think) N column - a code - hardcoded O column - a code - hardcoded P column - empty. This can be changed, I need to double-check with the client. Cheers!