I will state from the start that I am a little confused at what you are saying. So here is an answer, hoping it will help. lol
1) You need to make sure that in Preferences, Drafting, Dimension, Ordinate - The Positive Direction is set to "User Defined" and not "All" If it is not and the dimension is already on, let me know and I can tell you how to fix it rather than recreate them all if there are a lot of them.
2) If the dimension is already in place, if you double click the dimension (do not turn on the Ordinate dimesion function first), you will see the origin appear. There will be a small orange block in the center. You can click on that and a small function window will appear and you can change it from "All" to "User Defined".
Once the origin is set to User Defined, you can right click on either of the blue arrows and click on either, "Reverse Baseline Direction", or "Reverse Perpendicular Direction".
AS FOR THE REASSOCIATING -- If you double click an ordinate dimension, the Ordinate Function window will appear. Click on "Select Object" then just click where you want it attached.
If this is not what you are looking for, please let me know.