The Huret Rival had published limits of 30T maximum cog size and 28T maximum chain wrap. Bicycling magazine tested the Rival and found the maximum cog size to be correct, but that the stated maximum chain wrap was slightly conservative and that it could actually handle 30T.
It would appear that you cannot use the desired 32T, but you could go to 30T. Depending on the size of your small chainring, you may also be able to use a smaller version to obtain your desired gearing. A change to 30T should not require an incease in chain length unless it already set up with the absolute minimum chain length. Even then, it would only be a problem if you rode in the large/large combination, which is not recommended due to the extreme chain angle. If you can push the bottom of the cage forward by inch with the chain on the large/large combination, then there should be no problem.
However, always the test changes to gearing with the bicycle in a stand or the wheel supported off the ground. Use light hand pressure to turn the cranks slowly and check all the gears, If there's a problem, the derailleur will put up a fuss and you can back off before you break something. If you test it on the road, while riding, the load will probably be too heavy and youyr response to slow to prevent breaking something in the event of an incorrect set-up.
BTW, Bicycling judged the shifting performance of this derailleur to be "excellent".