A Codex Chapter of Space Marines tends to follow the strict organisation and doctrines as laid in the Codex Astartes. The Ultramarines are the quintessential example, and most of their Successor Chapters follow their structure. Other Chapters, like the Dark Angels, have relatively minor variations in their organization and ways of fighting. Yet others, like the Space Wolves, simply ignore the organization presented in the Codex Astartes and follow their own ways.
The variations a Codex Chapter can exhibit are generally ideological differences - for example, while the Codex Astartes makes provisions for hiding Chapter colours in the name of stealth, some Chapters stubbornly bear their colours, as they wish to proudly display their affiliations. Some variations are unintentional; for example, more recently established Chapters may not have access to Dreadnoughts or Terminators.