Best way to reverse interdomal sutures? What would be the most conservative method?

Your post raises the question as to why you want to reverse the effects of the tip sutures to begin with. I presume it's because the tip is too narrow or pointy. If the surgery was performed VERY recently (within weeks or so) and nothing else at all was done to the tip as you suggest, the most conservative approach would be to cut the suture transcutaneously with a hypodermic needle. Unfortunately, if any significant time has passed since surgery, scar tissue attachments will have formed between the domes making this simple approach highly likely to fail. Additionally, if ANY other alterations were done to the tip (dome division, crural overlays, tip grafts, camouflage grafts, etc.) this could worsen things. Almost always an overly narrowed tip will require going back to the operating room for a revision.
All the best,
--DCP
Pearson Facial Plastic Surgery®

It all will depend on the intraoperative findings, that's why the reoperation has to be done by a very good revision rhinoplasty expert with a vast portfolio of technical resources.
If the domal plication was done with permanent sutures (I personally don't use them, I dislike the risks and effects of the foreign body reaction, prefer temporary / dissolvable ones) the prognosis is worse, since it is likely there is necrosis and permanent kinks or deformations at the domes, with massive replacement of cartilage by fibrosis. 
If the domes are damaged, necrotic and replaced by fibrosis, or irreversibly reshaped (intraoperative tests can be carried to determine this extent), then restoring the original shape or building an alternative more harmonious one will require grafting to rebuild the domes and the tip (nothing specially difficult for revision rhinoplasty surgeons, a routine in my practice of tip revisions, I'd say).
Also, besides plication the surgeon may have performed trims, cuts, or plasties, poorly or brilliantly executed, precluding an spontaneous reversal of the shape.
Eventually the surgeon might have used dissolvable suture, refrained from aggressive maneuvers and the domes be feasible released from internal scarring to return to the original or close to original shape; should that be the case no grafting woudl be required.
If you wish better grounded opinion well lit, focused and standard images have to be assessed: frontal, both lateral and both oblique views, also underneath the nostrils.
Feel free to request any additional information from me.

In our practice for over a decade, we have used dissolvable stitches to sew the nasal tip cartilages together. Scar tissue holds them in that new anatomical  and narrow position. Cartilage grafting techniques will be required to try to widen the nasal tip if it's too narrow. It's important to know how much cartilage is left on the inside of the nose for potential grafting purposes. Revision rhinoplasty is much more difficult than a primary rhinoplasty due to previous alterations of the normal anatomy and scar tissue formation.