How did you want to search the customer and edit its record. By its name, id or something else? If you can store each customer information in one line then it might be easy to read text file line by line and parse each line and retrieve information.
NOTE:To modify anything in text file, you will need to read the entire file, row by row, saving it in memory with appropriate modifications, and rewrite the entire file.

You can also write a parser and load complete file at once and extract each customer information and store in a map, Manipulate your records in memory and save everything at once in a file.

Suggestion . Use XML if you really want to store information in text based files.