BOM validity end date not changeable

Hi Experts, we want to change in the validity period hence it is showing in grey field, when we are creating a BOM. This is our business requirement that we want to change the validity to 31.12.9999 by default, we want to change it according to our requirement. Please help us in this regards how we can make the validity period changeable. OSS connection has been opened. Thanks, Pratibha