How to modify .htm page attributes from outside the .htm?

I'm investigating an issue in our system. In BuPaDetail.htm of view ICCMP_BP_DETAIL/BuPaDetail, some custom code has been added. A flag called 'CHANGEABLE' with type abap_bool has been added. Within the .htm file, there is no code to modify the flag.

My question is, where can the code to set or reset the flag be located? or how can we modify page attributes added to the .htm from outside the .htm (like from the view controller implementation class)?

Many thanks,

Phil