Are you talking about reusing parts of an existing building? If yes you can refer to this support post: https://support.etoollcd.com/index.php/knowledgebase/model-existing-buildings/
If you’re talking about adjusting the recycled content of a material, we generally do not encourage this mainly because that manual adjustment may not be a good estimate of the impacts associated with the recycling process involved for that material. Swapping the material out with the recycled version of that material however is coming from the LCI dataset which is based on industry averages therefore more legit. Unfortunately, not all materials in the LCI dataset has recycled options exactly because there is not enough data on those materials being recycled in the mainstream.
The story is a bit different for steel though because it IS such a widely recycled product. However, if you did change the recycled content of steel, you’ll actually find that there is no change in the GWP. Please refer to this post on why: https://support.etoollcd.com/index.php/faq/standards/closed-loop-recycling-en15978-work/
Hope that answers your question.