Cad template customization

I need to create a software & it takes 2 inputs : 1- A DGN/CAD file as a template with some information like dimensions for example & i will replace those dimensions with a variables like $Length , @Width 2- An excel sheet with a number of supports with a fields contains data for those variables so the two inputs are a template with some variables & an excel sheet contains the values of these variables & the software mission is to generate the drawings after substituting the variables with their values so the whole idea again , i have an excel file with multi-Sheets each sheet contain a template name & each sheet contains set of variables & the software role is to search for these variable names in the template & replace it with the ones in the excel sheet Note: The template should be dynamic , I means that i can add any number of variables at anytime & add any template (add extra sheet to the excel file)