Considering your circuit, it would help if some explanation of it was given: -
IC1a, R1 and C form an integrator such that if the square wave (from IC1b) is in its negative half-cycle, there is a positive ramp on the triangle wave output. The ramp rate is dependent on the magnitude of the negative portion of the square wave. A more negative value creates a steeper slope in ramp; a smaller negative value creates a shallower ramp.
Likewise on the positive sections of the square wave; a larger positive value of the square wave creates a steeper negative slope; a smaller positive value of the square wave creates a shallower negative slope.
So, if the output of IC1b were somehow clamped to a smaller p-p voltage, the triangle wave output would take a longer to reach the trigger threshold point of IC1b (determined by R2 and R3 in my diagram). And it is this fact that can be used to create a variable frequency triangle wave whilst keeping the triangle wave amplitude stable.
Consider the voltage clamp circuit: -
On pin 5 is 3.3 volts but it doesn't have to be 3.3 volts - it could be "voltage controlled". If you duplicated this circuit for negative square wave excursions by reversing the diode and using a negative reference voltage, you have the ability to clamp a square wave from a very small value (say 200 mVp-p) to say 20 volts p-p. That's a 100:1 amplitude range and this will produce a frequency range of 100:1.
You need two reference voltages (one being the negative of the other) but, this is easily changed to a singlecontrol voltage by using another op-amp to invert the positive control reference voltage to a negative value: -
Can this circuit be modified for what I need
I think it's worth doing if only to learn from it. I'm not sure that 5 op-amps (including your original two plus the VCO input inverter) is as far as you would wish to go but it should work reasonably with half-decent op-amps on a +/- 15 volt rail and with a little effort and better choice of op-amp on a +/- 5 volt rail. Or use a modern version of the ICL8038 (35:1 range on frequency adjust).