You can do it without a flywheel holder and you might not effect your crank's truing.

can, might, should ... you never know.

To be on the safe side, use a metal bar with 2 screws through it as flywheel holder. There is a different thread where we did some torque/load calculations.

And: it's not only the crank that MIGHT suffer, also the conrod small ends MIGHT suffer from the pointy load.

There is a reason why Honda uses a flywheel holder and the tool which blocks the gear on the RHS to remove that nut.