Changes to prj.conf not propogating to autoconf.h

I'm trying to modify the lwm2m_client sample with my network APN and Operator details so am adding the following to prj.conf

CONFIG_LTE_PDP_CMD=y
CONFIG_LTE_PDP_CONTEXT="1,\"IP\",\"ep.inetd.gdsp\""
CONFIG_LTE_LOCK_PLMN=y
CONFIG_LTE_LOCK_PLMN_STRING="27201"

Making these changes and doing a "Build Solution" does not import these changes.

The only way I can get these values to be taken is to do "Open nRF Connect SDK project" and Select "Clean Build Directory"

Is there another way, or am I missing a step?

I have tried "Configure nRF SDK project" but there is a bug there which doesn't allow writing of PDP Context string - JSON error

Thanks!