What is the {0,1,1} part?
Can't we use LibRS option instead?
I mean replace for example
_hdr_cfg->set( RS2_OPTION_HDR_ENABLED, 0, { 0, 1, 1 } );
with
set_option(HDR_ENABLE, false)
?

I think that set_option is another level of abstract and that it is better to keep it here.

The interface requires a range, we supply { 0, 1, 1 } means on or off

I think it would be more clean if all the comments in this block will be replaced with one comment in the block head.
Something like this:
Changing exposure while HDR is enabled was requested by customers. It is currently disabled by D400 FW, so we workaround it by disabling HDR, changing exposure and enabling again. Disabling/Enabling resets the sequence index so we need to keep and restore it.

Done