Yz450f 350 map?

The rotating mass and torque of that engine will never let it feel like a 350. 

G2 throttle tamer made a nice improvement on that bike, it smooths out the initial throttle response and gives the rider more control.

You can change the power delivery quite a bit with mapping, in general changing the Fuel = Torque  and Ignition = Responsiveness 
Even if you subtract all the Fuel and Ignition it still won't feel like a 350 due to the gearing.

You'll have to go up a few teeth on the rear to get a 350 similar feel.  First gear is really tall on that bike, I think in stock form you could hit 35mph in first gear.  It'll clear up to a 53t.   Probably a 51 or 52 would work best for a "350 feel", but you'll have to try it and see.
 

Don't know why you got down voted man, you're dead right lol.

It won't feel like a 350, it will just feel like a slow 450 with all the same traits you are perceiving as negative. 

I totally understand what you're wanting, and it would be amazing if possible. Yamaha would be printing money with a YZ350. 

I know my truth 😂

I haven’t used the Yamaha tuner app, but if your able to remove timing in the lower rpms do that. Should make it feel softer/slower/less powerful off the rip. Good luck and have fun getting back into it!

Twisted development has great maps to time the bike down. Heavier flywheel also will help

I also just got back into riding after 13 years. 2019 yz450f. I use this map and it is very smooth. Easy to ride.

I’ve been running a traction map in a Vortex/500EXC for a couple months, it’s amazing how smooth and controllable it is compared to the more aggressive maps. At about 1/3 throttle it comes alive and starts pulling harder. Totally not a direct comparison, but mapping has a big effect.

I just installed my flywheel from Bundybuilt. I hope it’s what I need.