Could bone marrow transplants help make xenotransplants viable?
I feel I've enough sources &amp; data to venture an answer on this one myself now, so here goes.
Step one: Can we produce the pig in the first place?

Fetal Inoculation With Donor Cells in Cardiac
Xenotransplantation 1996
Perinatal induction of immunotolerance to cardiac and pulmonary allografts July 1997
Induction of donor-specific tolerance to cardiac xenografts in utero: 1998 Sep
Cell Transplantation January 1 2003
IMMUNO-INTERVENTION FOR THE INDUCTION OF TRANSPLANTATION TOLERANCE THROUGH MIXED CHIMERISM: 2011 Aug 11
In utero hematopoietic cell transplantation: induction of donor specific immune tolerance and postnatal transplants: 2014 Nov 12

another link to the same article
In utero hematopoietic cell transplantation: induction of donor specific immune tolerance and postnatal transplants 12 November 2014

First human-pig 'chimera' created in milestone study 26 Jan 2017
Interspecies Chimerism with Mammalian Pluripotent Stem Cells 2018 Jan 26
Interspecies Chimeras and the Generation of Humanized Organs 3 Jan 2019

Yes, an animal can be produced with donor specific tolerance to the patients organs, it's a known procedure &amp; observed effect that has been replicated numerous times in experiments, its immune system would not attack either the patients cells or its own.
Step two : Can we transplant this animals bone marrow to the patient?

Stem cell and bone marrow transplants

Yes, bone marrow transplants involving the complete removal of the original bone marrow is a long established procedure for the treatment of leukaemia.

And now being used for treatment of other severe autoimmune diseases in a way which may make this idea moot, I'll have to look into that further, not read that article in full yet.

Step three : Will we then be able to transplant other organs from this (or a genetically identical) animal to the patient without tissue rejection?
The immune system isn't seated entirely in the bone marrow &amp; its products (the thymus, spleen &amp; lymphatic system also have roles) so for best results some of these may also need to be replaced.
If so it must be hopped the lymph nodes play no role in in the development &amp; tuning of the immune system, there are 500-600 of them around the body so replacing them all would be no small task.
Conclusion :
Still in progress / just saving work so far