When the copy feature in article management is utilized, the new article that is created in the destination Knowledgebase (KB) will have a new article ID. There is currently no method to move articles (as opposed to copying articles) from one KB to another while retaining the original article ID in both places. This is by design.
How to copy an article:
1. On the Article Management page, select the check box(es) to the left of the Article(s) to be copied.
2. Click 
from the Article Management toolbar. A message box is displayed which prompts confirmation of the copying of the Article(s).
The Copy Articles Confirmation Dialog Box
3. Click OK.
The Target Knowledge Base page is displayed.
The Target Knowledge Base Page
4. From the Knowledge Base list, select the destination Knowledgebase where the copy of the article(s) should be placed.
5. Click Copy. The Article(s) are copied to the selected Knowledgebase.
Note : After article(s) are chosen to be copied the article(s) are placed in a queue that runs on a scheduled basis. You may have to wait for up to 10 minutes for the copied article(s) to be listed and displayed in the destination Knowledgebase.
This general information can be found in the Administrative User Guide available on the Support Site. Please review Chapter 3 - Managing Content to learn more about this.