The Pt100 temperature sensor delivered with my PreSens meter is too large for my measurement set-up. Can I use another smaller temperature sensor with this device?

As long as it is a 4-wire temperature sensor, every Pt100 sensor can be used with the PreSens meter. However, the fitting connector may have to be attached to this sensor. PreSens can provide the correct connector parts, so the temperature sensor can be connected to your device.
(A detailed instruction on how to attach the correct connector to a 4-wire Pt100 temperature sensor can be found in the Fibox 4 instruction manual IM_FB4-FB4trace chapter 6.5.)