when i was playin around with the first silkroad privateservers in the past, i've allways prefered the way of directly injecting the asm hex pattern to the client.
for just in time acting, you'll have to use simple asm logics, to redirect stuff, to static positions, or even realy react just in time.
for example, to send packets to the server, only using autoit, i was calling the ingame sit-function (was the easiest one, since there were no parameters used in it), and wrote an asm logic to overwrite the build packet by my own one, before it got send. that way i didn't have to mess around with encrypting stuff...
when i stoped developing, it looked like this:
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