Create change file in geographical boundaries with osmupdate

Yes it is possible, but it is a bit more complicated.

First you update your extract with osmupdate:

osmupdate germany-latest.osm.pbf germany-updated.osm.pbf -B=germany.poly

Then you calculate the differences with osmconvert:

osmconvert germany-updated.osm.pbf germany-latest.osm.pbf --diff --fake-lonlat --emulate-osmosis -o=diff.osc

This gies you the desired osm change file. After that you probably want to rename germany-updated.osm.pbf to germany-latest.osm.pbf to be able to run the same process again to get the next diff.

It has a slight problem though: you might get incomplete extracts when ways or relations move inside your boundary. This is why I do a slightly more complicated variant for the swiss extract on planet.osm.ch:

use a larger bbox around swizerland:

BBOX="5,45.3,11.3,48.3"

update this bbox:

osmupdate chbbox_updated.o5m chbbox.o5m --minutely -b=$BBOX

cut out switzerland from this larger region:

osmconvert chbbox_updated.o5m -B=$CHPOLY -o=switzerland_updated.o5m

and create the diff between the old cut out and the new one:

osmconvert switzerland_updated.o5m switzerland.o5m --diff --fake-lonlat --emulate-osmosis -o=diff.osc