Hello,

Are there F12 signs on the streets you changed?
https://www.wegcode.be/media/image/orig/2e642ae51c3fbc4b0adc54c012013014e236cecb.png

In that case, the correct way to do this in OSM is not just to change the maxspeed but also to change the road type.  It must become highway=living_street.  This is because this roadsign implies other rules, not just a lower speed.

Thanks.