Is it okay to use 'Having been+third form' as the reduction of Passive Relative Clause in Simple Past Tense in order to put more emphasis?
In a word, no—because BE having been VERBPaPpl is not a valid English construction.
(In what follows, * marks the following utterance as ungrammatical.)
There is a very strict rule governing the sequence of auxiliary verbs, one piece of which is that auxiliary HAVE cannot be cast in the progressive construction. We cannot, for instance, say
*The actor is having been chosen for the role or
*The contestants were having been considered adequate.
(Lexical HAVE can be cast in the progressive—okI am having a good time—but auxiliary HAVE cannot.)
The sort of reduction you're talking about is called 'Whiz reduction': it involves deleting a wh= relativizer and a following form of BE:
who was chosen
who were considered adequate.
Consequently, your proposed sentences represent 'Whiz-reduction' of illegitimate unreduced forms:
who was having been selected
who were having been considered adequate.
You can, however, use having been VERBPaPpl in contexts where preceding BE is not implied—typically as a supplemental participle clause:
Having been selected for the role, the actor is now looking for a suitable costume.
In this case having is not a component of a progressive construction but an ordinary present participle. The clause having been selected... is not an adjunct ('modifier')—it doesn't just tell you which actor is being talked about. It is a supplement: it makes a separate assertion about the actor. It represents an underlying The actor has been selected, with has cast as a present participle so the clause can be 'attached' to the main clause as a subordinate. The perfect construction indicates that this event, the actor's selection, took place before the action of the main clause.
And this sort of subordinate participle clause can also be moved into the position where you have put it in your rewrites; but it must be 'bracketed off' from the main clause with commas, to mark it as a supplement, not an adjunct:
, having been chosen for the role
, is looking for a suitable costume now