CMOS Output Sensor with a pull up resistor
There is no problem with adding a pull-up resistor to the output as long as you don't exceed the current sinking capability of the CMOS driver.

The MH251 has a abs max output current of 1mA according to the datasheet, so your pull-up resistor must conduct less than this valu when Vcc is applied over it. For safety you want some margin, so lets say a max of 0.5mA. For a 3.3V supply, that gives \$R &gt;&gt; V/I=3.3V/0.5mA=6.6k\Omega\$. Something like a \$10k\Omega\$ pull-up should be fine.



Of course, even if you add the footprint for the pull-up resistor to the design, there is no requirement to populate it with a component.

When using the open-collector chip populate the footprint with the necessary resistor. Otherwise leave it unpopulated/DNI for the push-pull chip.