Is it permissible to agree with the first wife, after marrying a second, to change their separation into a normal life with her, in a manner less than equally?

The spouses must avoid separation and leaving the woman in suspense. It is either to hold together with kindness or to release with goodness, as Allah Almighty commanded: {And when you divorce women and they have fulfilled their term, then either retain them with kindness or release them with kindness}. Care must be taken to ensure the stability of married life and avoid problems. If the wife agrees to waive some of her rights, she may do so, as Sawdah (may Allah be pleased with her) did with Aisha (may Allah be pleased with her).