Custom Symbol - script to modify custom symbol and reset existing history

The attached simple script (sTestComb.mq5) reads a txt file and uses this as a basis to update the "SYMBOL_FORMULA" for a custom symbol.  The problem I have is the existing history is NOT updated.

The job is to create a script that will:

1. Read the attached GComb.txt file from the files directory and update the "SYMBOL_FORMULA" based on it. 

            Custom Symbol should be called "CombG", based on a FOREX major pair.  

            Custom Symbol should only be updated, not created from new.

2. Delete the old history and build a new history for the custom symbol based on the updated formula from the GComb.txt file. 

Note1: Please ensure that event handling is covered in the script.

Note2: The same script will be run multiple times per day updating the same Custom symbol (CombG). 

References: 

https://www.mql5.com/en/articles/8226 (CUSTOM SYMBOLS: PRACTICAL BASICS)

https://www.mql5.com/en/code/18855 (Symbol - library for MetaTrader 5)