Maybe you have to sign into the project with Exclusive Access.
You can create new attributes but can modify existing ones only when signed in with Exclusive Access.
TW2, available from AC13 is fully flexible in this respect.
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AMD Ryzen9 5900X CPU, 64 GB RAM 3600 MHz, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), Windows 10 PRO ENG, Ac20-Ac28