Dear Devi
any property tree (including the nodes) is defined in customizing. Therefore: this is nothing on the fly which you can do here (only by using customizing)
a.) you should not change the "STANDARD" tree; recommended is to create "ZSTANDARD" as a copy or something like this and use the cusomizing properly to adapt the new tree.
b.) therefore: you can add a node within one day if you know which customizing activities is important etc; the same is true for deletion of a node
You need to differentiate between "node" and new value assignment type (property), the actiivities to be done in SPRO (IMG) are different (and there are further manual steps required).
The whole process is absolut standard and nothing "tricky" as long as you know what you are doing.
To my knowledge: there is no OSS note which is really related to this topic.
The best way is to "learn" first the SAP Standard set up (and how is it done in IMG) and then do it by your own. But if you create a new value assignment type (property) more steps are involved which you need to take care.
C.B.