Yes, you need to change all of your assets to match the Cost Seg on your 2024 return.
You need to add EACH of the 'new' (separated) assets. It will likely be a long list to match your Cost Seg.
You also need to modify/correct the existing asset (such as the building) that are changing. For the previous asset (the building) you will change the Basis/Cost to reflect the new amount that Cost Seg shows (a smaller amount, because the other assets were removed from it) and you will change the "Prior Depreciation" to match the Cost Seg (a smaller amount, because the Basis/Cost is smaller). It will not be either $100k or $300k.
