How to use reset pin of ATmega64
My theory is that if I &quot;pull low&quot; (ground) the reset pin (easiest attach point being the reset side of the resistor) via a momentary switch I can generate that reset signal. Is this correct?

Yes. No need to do extra stuff. So, ...

Do I need to open the circuit between reset and VCC?

... no, and...

Should I include a resistor between the reset pin and ground to be a current limiter?

... no.
But resetting the MCU may not be a 100% solution as the main cause of lockup could be something else (e.g. parasitics, fluctuations/spikes/unwanted noise along the supply line, heat, etc.). So maybe you should find the cause of lockup.