In order to apply the custom library please follow the below steps :
Obtain your custom library from Access.
Close Dimensions if it is open.
Navigate to your installation location for Dimensions by default this is C:\Program Files (x86)\Access Applications\Dimensions\Accounts\(version number)
Locate the original Access.lbr file and rename it.
Copy and paste the new custom library file into the above folder location.
Open Dimensions.