To comply with the latest IEC regulations, the UT61E would need to have HRC fuses rated for the highest voltage category of the meter. In this case 1000V. The fuse breaking capacity would have to be equal to 50kA or at least 1000V divided by the impedance of shunt and test leads, which comes to about 5kA. Fuses would have to be FF rated (very fast blow).
It not just a case of replacing fuses either, internal clearances and PCB trace creepage would have to comply with the more stringent IEC requirements (8mm creepage for CAT III 1000V), as the CAT rating goes up.
Provided test leads would need to be changed, as no metal can show on the probe, except for the very contact tip.