I would argue that 'assimilation' should be defined as respecting the constitution, systems and processes in place in a nation that one lives in.
However, most democratic political systems also allow for 'amendments to the constitution' and 'changes to existing laws, systems and processes' through constitutionally defined means - so while one should respect existing laws and the constitution, that does not mean that one cannot advocate and campaign, legally and constitutionally, for changes to the existing constitution and laws.
'Adopting native cultural and society norms' should not be considered an essential part of 'assimilation' in the context we are using. Wearing a burqa, hijab, headscarf, turban etc. (or not) should not be considered as 'alien' or damaging to a nation where the socio-cultural norms are more liberal and non-religious. That said, refusing to remove a Burqa/face covering in order for identification documents to be made definitely falls in the category of not respecting local laws and processes.
Agree. Amendments may be required in the USA but in the UK there isnt a need as the constitution is unwritten - and there are and have been examples where for example sikhs that have wanted to join the police or fire services have been allowed to wear their turbans hence its now the norm and accepted