Update:

regarding the display of the local host info. I have 'played around' with the settings in Tools, Options, Connect, Options and have tried every combination possible, All that is affected there is how the information is collected and, as a result, it still displays. It is the displaying of that info that I want to mask, irrespective of which method mIRC uses to obtain it.

Slight tie in withe the on Connect query; I have found that this host name: message is sent from the mIRC client just after end of MotD (raw 376) so that may be it's 'trigger'. irrespective of the server/network user count info being displayed before or after MotD.

Further to this the message will never show up in any debug session since it not sent or recieved from the server. This makes it extremely hard to see what any possible trigger is. The only way I found to locaate it was with the old
Code:
raw *:*: { echo 6 -st raw event debugger: $network raw $numeric : (1) $1 (2) $2 (3) $3 (4) $4 (5) $5 (6-) $6- }

which displays in the status window (echo 6 -st) so I can see what happens immedietly before and after the message.

Thankfully I had lots of these (and debug sesssion) saved as log files.