UMLR — Please provide more detail on redefinition

I am attempting to implement support for UML 2.5.1.
When handling property redefinition based on the uml Abstract Syntax Metamodel.xmi :
Given this sort of construct in the xmi..(newproperty, baseproperty xmi:ids added for reference in my question below)
<ownedAttribute xmi:type="uml:Property" xmi:id="newproperty"..">
<redefinedProperty xmi:idref="baseproperty"/>
I need to understand whether it is correct to..
a) assume that newproperty is being defined from scratch (meaning: clean slate; a brand new property)
or b) the property being redefined (baseproperty) should be adjusted based on what changes are specified in the xmi

In our current implementation it is rather difficult for us to accommodate a change in name of the existing property so I propose that newproperty is a subset baseproperty, with the additional restriction on baseproperty that it becomes a derived union.
This paper..
"On the Relationships Between Subsetting,Redefinition and Association Specialization"
https://uni-koblenz.de/~ist/documents/Bildhauer2010OTR.pdf
.. although based on material dated 2006 (UML2.2), this discussed UML property redefinition in comparison to subsetting and judged that redefinition was subsetting with a constraint.