Changing bonnet release cables is a tedious job! Getting the grommet in the firewall back in place needs the eyesight of a hawk, the flexibility of a teenager and the patience of a saint, none of which I have!
Adjusting the bonnet pins correctly took a while. I started with the pins loose (ish) on mounting plates and slathered in Engineers Blue to get them centred (they weren't!). Went to undo locknuts to deal with depth of penetration (quiet at the back you!) and found the locknut on the stuck side wasn't locked and had allowed the pin, over time, to screw itself back in, making that side a tighter and tighter fit, until ultimately it wouldn't unlatch.
Ah well, nice to know what caused it!
Have once again brought original door handle/ lock home and am definitely going to fit the cam kit tonight. Cut the extraneous metal tag off while at workshop so only have the cleanish fiddly cam to replace. I know how to have fun on a Friday night!