how to change the diagnosign in lightline?

Use CocDiagnosticChange (check :h CocDiagnosticChange) to call lightline#update() to refresh lightline when there's new diagnostics. Check wiki information and lightline docs. As for setting symbols, this is a question for lightline documentation.
Checkout :h coc-status-manual
fix this by let g:coc_status_error_sign = 'E:'
None of these suggestions work. I want the feedback (using lightline, coc#status works in it), however, on the mac these characters use up two widths, causing statusline length calculations to be off by one, and completely breaking neovim rendering.
I will note that regular vim does not break as badly here. This is sorta neovim specific. It may also be tmux specific.
But we need a way to configure this...
You can create function yourself by make use exported variable
I think i complained too soon, sorry about that. It's a bit tough to really get down to what's causing the problem. I will test more without the status showing and also try to make a basic custom status function.