hi, i just replaced the top clamp along with the bars and levers on my 2020 wr250r which requires removal of the ignition barrel from the oem clamp which it's inexplicably attached to with two "tamper-proof" bolts. i came here first and found several threads where folks were talking about cutting the bracket off or punching out the old bolts.
if you go ahead and remove the stem nut and fork pinch bolts (which i did because i was replacing the clamp anyway) you can flip the whole top clamp over and take a hacksaw to the bolt at the joint between the ignition barrel and oem clamp. i think that's the neatest way to do it without special tools and if your bike was put together like mine you'll want to torque the stem and triple clamp nuts properly anyways. put some newspaper or something underneath the clamp while work to keep the metal shavings from getting everywhere including stuck in the fork seals.