@Harper gave an excellent answer as to what you should do instead. But here is the reason why you can't just implement your original plan:
Wires and connectors are rated based on current. (Voltage too, but at this level, current is the concern.) Almost certainly the wires coming from the meter to the 100 Amp breakers are rated for 100 Amp (or possibly a little more) but not for 200 Amp. It is possible that the connectors on the meter are rated for 200 Amp, but it is quite likely that they are also not rated for 200 Amp (or more likely, not designed to hold the really big wires needed for 200 Amp).
If everything were always perfect, this would not be a problem. Power would flow equally on both wires, both in and out of the transfer switch, and everything would be OK. However, there are two potential problems:
- Differences between the wires
If the wires between the meter and the transfer switch, despite being nominally the same, have significantly different resistance, they will carry different amounts of current. The result, in a high usage (i.e., close to 200 Amp) situation, will be that one wire will carry more than 100 Amp. Since the protection is downstream of the transfer switch, nothing will prevent the > 100 Amp wire from overheating.
This is the more clearly dangerous situation. If a wire in either pair breaks, the other wire will carry the full current - possibly as much as 200 Amp. The transfer switch to breakers part will be protected by the 100 Amp breaker (though this would still not be a good situation). But if one of the wires between the meter and the transfer switch breaks (or more likely, a connection gets a little loose), there is nothing to prevent all the current going on the other wire.
There are some very limited, very high current, situations where this type of paralleling is permitted, but not normally in residential construction.