You say FLV but what you describe sounde like a swf. If you have the flash authoring environment you need the FLA that created the SWF. For Flex you generate swf's through mxml files that can be edited through flex builder.
Yes its playing FLV in SWF.
See its golf movie people will upload from simple form
and in admin i will run my flash swf file where that flv movie play and
i can be able to edit that that means i am able to draw line and remove
anything if i wish ... or add anything ... in flv in run time environment.
You can overlay the FLV that's no problem but you would still need to have the original FLA. If you actially want to edit The FLV you would need to use a video editing program to access individual frames and to make the kind of changes you are talking you would have to edit it frame by frame probably with a bitmap editor like photoshop. It can be done but would you relly want to.