How are the CPM files modified by SPI?

I notice that the CPM file has the line at the top:

{ Machine generated file created by SPI }
{ Last modified was 12:44:53 Friday, January 28, 2022 }
{ NOTE: Do not modify the contents of this file. If this is regenerated by }
{       SPI, your modifications will be overwritten. }

I need to change a variable in the CPM file or DE and the atdm.ini file in code. How would I find and replace specific variables in these files programmatically?

In the atdm.ini file I need to change a vairable 'xxx_legalname = YYYYY'

and in the CPM:

START_CUSTOMVAR
LEGAL_NAME 'A Division of YYYYY Limited'