What does this Op-Amp circuit do?
This circuit is a precision constant current source for the PT100 (R30 in the schematic).  This is a Howland current source (principles of operation here).

If you use as is it with PT1000, it would work in general.  You might see  more self-heating.  The output would rail at a lower temperature.

The current is inverse-proportional to R3x**.  You can reduce the current by increasing R3x. 

** The designator is obscured by the black circle.  The resistor is directly above JP18.