I like your user name!!
You decide that when you put the asset into service and you make the election. But once it's done, you can't change it.
Which Depreciation Method Applies?
MACRS provides three depreciation methods under GDS and one depreciation method under ADS.
The 200% declining balance method over a GDS recovery period.
The 150% declining balance method over a GDS recovery period.
The straight line method over a GDS recovery period.
The straight line method over an ADS recovery period.
For property placed in service before 1999, you could have elected the 150% declining balance method using the ADS recovery periods for certain property classes. If you made this election, continue to use the same method and recovery period for that property.
Table 4–1 lists the types of property you can depreciate under each method. It also gives a brief explanation of the method, including any benefits that may apply.
Depreciation Methods for Farm Property
If you place personal property in service in a farming business after 1988, you generally must depreciate it under GDS using the 150% declining balance method unless you are a farmer who must depreciate the property under ADS using the straight line method or you elect to depreciate the property under GDS or ADS using the straight line method. You can depreciate real property using the straight line method under either GDS or ADS.
Fruit or nut trees and vines. Depreciate trees and vines bearing fruit or nuts under GDS using the straight line method over a recovery period of 10 years.
ADS required for some farmers. If you elect not to apply the uniform capitalization rules to any plant produced in your farming business, you must use ADS. You must use ADS for all property you place in service in any year the election is in effect. See the regulations under section 263A of the Internal Revenue Code for information on the uniform capitalization rules that apply to farm property.
Electing a Different Method
As shown in Table 4–1 , you can elect a different method for depreciation for certain types of property. You must make the election by the due date of the return (including extensions) for the year you placed the property in service. However, if you timely filed your return for the year without making the election, you still can make the election by filing an amended return within 6 months of the due date of the return (excluding extensions). Attach the election to the amended return and write “Filed pursuant to section 301.9100-2” on the election statement. File the amended return at the same address you filed the original return. Once you make the election, you cannot change it.
https://www.irs.gov/publications/p946/ch04.html
Here is the link to the IRS publication on DRD's. I've been reading about installment sales and bankruptcy all freaking day long, so I'm afraid you are going to have to wade through this one on your own.
https://www.irs.gov/instructions/i1120c/ch02.html
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