Rather than taking the full purchase price and reporting it as one asset being depreciated over 27.5 or 39 years, you can figure out the individual assets within the purchase and break up the purchase price into many smaller assets.  For example, driveways, sidewalks, and fences could be land improvements that are depreciated over 15 years (and could qualify for Bonus).

While the client could try to figure out and break that up on their own, a Cost Seg is a specialized report from a company that is highly experienced in breaking it up, so that is usually what most people do.  The Cost Seg breaks it up into many assets and shows the cost/value of each individual asset.  You would enter each of those assets into ProSeries.

Yes, *IF* the property is non-passive, using the Cost Seg for quicker depreciation can create a rental loss that can offset other income, such as a W-2.  If the rental is passive, a Cost Seg might not be as advantageous because the losses may be 'trapped' under the Passive Loss rules.

If it is a retroactive Cost Seg that you have already filed ONE tax return, just amend the prior tax return.  If you have already filed two or more tax returns, in my opinion you would need to file Form 3115 with the current return to add the new assets, AND you would need to amend the prior returns to correct the Basis of the building (you reported the full amount, rather than the building-only amount with the other assets removed).