Error message: “System Status CLSD is Active” occur for transactions that involve internal order.
Business Scenario:
Assuming the company incurred costs and expenses and capitalized those. Those expenses are temporarily posted to an internal order e.g. 1234. Later on during the year, the accumulated costs and expenses posted in internal order 1234 settled to an asset.  Let’s say [...]

Listed are SAP standard transaction codes in SPRO under Cost Center Accounting:
»» OKKP - Activate Cost Center Accounting in Controlling Area
»» OOAP - Activate Cost Center Accounting in Controlling Area
»» KEOC1 - Enter Settings for Enterprise Organization 
»» KEOC - Create Enterprise Organization
»» OMGEN - Generate Enterprise Organization from Standard Hierarchy
»» KEOG - Generate Enterprise Organization from Standard Hierarchy
»» [...]

Can we change the reconciliation account in the vendor master data after transaction(s) have been posted to the vendor?
YES, the reconciliation account can still be changed. However, there are some prerequisites that need to be done first. I’d like to share the configuration changes and procedures:
A. Set the “Reconciliation Account” field in the vendor master as [...]

Listed are SAP standard transaction codes in SPRO under Cost Element Accounting:
»» OKB2 - Make Default Settings
»» OKB3 - Create Batch Input Session
»» SM35 - Create Batch Input Session 
»» KA02 - Create Cost Elements
»» KM5V - Create Selection Variants for Cost Elements
»» KAH2 - Create Cost Element Groups
»» OKA6 - Define Cost Element Attributes
»» OKA4 - Define Cost Element [...]

What’s the assignment rule of profit center to cost center, and vise versa?
A profit center can be assigned to 1 or more cost centers (1:1 or 1:n). Meaning, many cost centers can use the same profit center. All postings to the cost centers are posted statistically to the profit center assigned. Here’s an actual screen shot of the [...]