|I know this might not be what you are wanting, but it might be easier to load the file into word and do a find/replace.|
Find 000 Replace with 020
Find a _ Replace with a _KL_
Then simply save the file as text to whatever name you like.
So far as I know, Batch language is too limited to do a line by line read and accomplish what you're wanting here. You could try setting a macro in Excel or Word, or research extended batch, but for now the above would be a simple temporary solution.