Changing eeprom values mid-print?(+a bonus question)

Is it possible to change eeprom acceleration values mid-print through gcode commands M201 or M204? Or Do I have to restart the printer or the print for the changes to take effect? If so, is restarting the print sufficient or do I have to restart the printer itself? I want this because I want to see the effect of different acceleration values on the print without starting a new print for every value.

Bonus questions:

Are the ripples on Jupiter and the Saturn's rings caused by the stepper driver not driving the stepper smoothly?

[imgur.com]

If so, should reducing or increasing the vref on the x and y drivers reduce the ripples? I did try different vref values between 0.5 and 0.9 volts but I didn't really see any noticeable difference. What I did notice is that decreasing the vref below 0.7 volts introduces really harsh resonating bearing noises during moves.

My x and y steppers are bot 1.02 amps and I've set the vref to 0.8 volts. Do you guys recommend reducing or increasing the vref? The motors don't get warm at all so I don't think 0.8 volts is too much.

Edited 2 time(s). Last edit at 05/15/2017 08:01AM by Nadim.

Yes you can change m201 or m204 any any time.. but there is a small buffer, so don’t expect instantaneous changes

This doesn’t change the eeprom setting though, not till you do a m500

re the ring ripples, are you talking about the ringing (can see almost shadows of the edges repeated again) or the over all surface effect?

Edited 1 time(s). Last edit at 05/15/2017 08:15AM by Dust.

Ok so M201 and M204 immediately take effect? Yes I do have to enter M500 to actually save it in eeprom so it persists after a restart. By the ripples I mean the overal surface effect.

As you noticed, I also have some ringing issues. I know the ringing on the edges is a mechanical issues, but I didn't manage to eliminate it. I did tension the belt and reduced acceleration to 800 and jerk to 8 in marlin, but this didn't change anything. The one thing I didn't try that I want to is to use a different stepper motor, because I've read that the ringing can also be caused by 'springiness" of the stepper motor shaft. I have a prusa design printer which has a aluminium bed with a 3mm thick sheet of glass on it. Maybe it's just not possible to eliminate the ringing on the edges with that amount of mass moving?

Could be bearing noise as well. I made a new extruder carriage that puts different forces on the system and the ringing seems to have settled down a bit.