How to edit standalone.xml file dynamically in keycloak

First, it seems in a docker container by default standalone-ha.xml is used. You can find this in /opt/jboss/tools/docker-entrypoint.sh. Second, I think after changing configuration file you'll have to restart keycloak server (container).

Not sure what do you mean by "dynamically". But it will be easier to modify the file locally and build a custom docker image. Dockerfile may look like:

FROM jboss/keycloak:6.0.1
ADD <path on your system>/standalone-ha.xml /opt/jboss/keycloak/standalone/configuration/standalone-ha.xml

Might be a little late . but I found out you can edit on the dockerfile.

FROM quay.io/keycloak/keycloak:11.0.0

RUN sed -i -E "s/(<staticMaxAge>)2592000(<\/staticMaxAge>)/\1\-1\2/" /opt/jboss/keycloak/standalone/configuration/standalone.xml
RUN sed -i -E "s/(<cacheThemes>)true(<\/cacheThemes>)/\1false\2/" /opt/jboss/keycloak/standalone/configuration/standalone.xml
RUN sed -i -E "s/(<cacheTemplates>)true(<\/cacheTemplates>)/\1false\2/" /opt/jboss/keycloak/standalone/configuration/standalone.xml

RUN sed -i -E "s/(<staticMaxAge>)2592000(<\/staticMaxAge>)/\1\-1\2/" /opt/jboss/keycloak/standalone/configuration/standalone-ha.xml
RUN sed -i -E "s/(<cacheThemes>)true(<\/cacheThemes>)/\1false\2/" /opt/jboss/keycloak/standalone/configuration/standalone-ha.xml
RUN sed -i -E "s/(<cacheTemplates>)true(<\/cacheTemplates>)/\1false\2/" /opt/jboss/keycloak/standalone/configuration/standalone-ha.xml

ref : https://github.com/anthonny/kit-keycloak-theme/blob/master/Dockerfile