overwrite ctrl_gen.mdx

how i can overwrite file ctrl_gen.mdx, part of mdx.dll?

.copy -o update\ctrl_gen.mdx system\dll\ctrl_gen.mdx

but, above command doesn't work like what i want.

i used it in progressbar, for live-update features.
with Remove function, i unload mdx.dll from mirc
memory to make sure mdx.dll is removed for a while
before overwrite with new file, but ctrl_gen.mdx is
still used.

anyone have idea?