The chapter and verse numbers your quoted do not match what's in the actual scriptures. You're off by one.
Actually it's quoted this way:
John 7:38 (New International Version, ©2010)
38 Whoever believes in me, as Scripture has said, rivers of living water will flow from within them."
John 7:39 (New International Version, ©2010)
39 By this he meant the Spirit, whom those who believed in him were later to receive. Up to that time the Spirit had not been given, since Jesus had not yet been glorified.
Now onto what I have discerned.
John 15:26 "But I will send you the Advocate--the Spirit of truth. He will come to you from the Father and will testify all about me."
This scripture would seem to disprove your above statement that the Holy Spirit and Christ are one and the same.
Jesus is speaking about the Holy Spirit in the third person, rather than in the first. If the Holy Spirit is indeed Christ then Jesus would have merely said he himself would return.
What the verses are seeming to indicate to me is not so much that Jesus becomes the Holy Spirit, but rather he is given his own to portion as he sees fit. When on earth in human form, he dispensed the HS that had been given to him by God.
When he ascended it seems to be saying that when he was glorified he received his own personal type of power. Remember that in John 1:1 we read that all things were created through Christ (using YHWH"s power or Holy Spirit) yet when Jesus ascends and is glorified he becomes a god all his own, yet still submits himself to YHWH.
John 5: 25-29 "Most truly I say to YOU, The hour is coming, and it is now, when the dead will hear the voice of the Son of God and those who have given heed will live. 26 For just as the Father has life in himself, so he has granted also to the Son to have life in himself. 27 And he has given him authority to do judging, because Son of man he is. 28 Do not marvel at this, because the hour is coming in which all those in the memorial tombs will hear his voice 29 and come out, those who did good things to a resurrection of life, those who practiced vile things to a resurrection of judgment. 30 I cannot do a single thing of my own initiative; just as I hear, I judge; and the judgment that I render is righteous, because I seek, not my own will, but the will of him that sent me.
After his resurrection Jesus proclaimed to his disciples that:
Matthew 28:18 "Then Jesus came to them and said, "All authority in heaven and on earth has been given to me."
These scriptures would seem to convey the message that after Jesus ascended to heaven and was glorified, he received his own personal type of Holy Spirit and while not seeking to do his own will, but that of YHWH"s, he sends it out and apportions it to others as he sees fit.