Nowadays two-way radios are getting more and more powerful, coverage
up to 8, 10 12 or more miles. Ironically, it is even harder to buy one
with only 2-mile distance.

I want to use a two radio just for short distance, for example, only
within 1000 feet. How to modify the circuit (generally speaking) so I
can extend the radio's powerful consumption? As I do not need it to
communicate for longer distance, I want it to reduce power output, so
I can use it for longer time. I know it is difficult to illustrate
without a schematics, but just in general terms, what kind of options
or in what areas can I do the modification?

One of my applications is to use 2-way radio as baby monitor for
longer distance than normal baby monitor does.