I want to downsize my new 425cc implants to 300cc. I have perky breasts but thin skin. Is this an easy procedure?

It's unfortunate you aren't fully satisfied so soon after your initial surgery.  I am inferring these are saline implants on top of your muscle.  If you want to be smaller and have less rippling, downsizing to gel is a good idea and a plane switch (to under muscle) should be considered.  This is best for an in-person consultation.  I would advise a consult with a practice that likes secondary breast cases, and plan on saving for a re-augmentation to gel with lift.  If a lesser procedure is acceptable for you, all you would have done is over-saved, which is a good thing!

When downsizing implants, the skin has to shrink a bit or there will be sagging. One thing you can do to help it is to have the implants intentionally deflated. It's an in-office procedure, and then over the next few weeks the pocket and skin will shrink. The new implants should be a higher cohesivity type such as Sientra of Allergan Soft Touch, and the base diameter and profile will be important to minimize rippling. Some patients need Strattice or Galaflex to add coverage.

There is nothing easy about performing surgery on qualified patients. If your Surgeon determines that your pockets are adequate you could explant and replace at the time when you're ready.

If the implant pocket is over expanded, and the downsizing would result in tissue laxity, it can get quite complex.  Sometimes, you need to plicate the pocket, add Strattice to reduce ripples, change the implant, and do some form of mastopexy.  Other times, it can be as simple as a implant exchange.You'll need an in-person evaluation to determine where you fall on the spectrum.

In general downsizing a modest amount (less than 150 cc) will not result in sag, and although the pocket ( capsule) needs to be adjust slightly should be an easier recovery and no more time in surgery than the original augmentation. You do have some visible rippling when you bend over which is common with thin tissues. That would not likely get better unless you added a piece of acellular dermal matrix (ADM) which adds time and expense to the procedure.  You have a nice shape, and you have reasonable goals.

If you have no capsular contraction, this should be a very easy procedure. With a capsular contracture (encapsulation), which you could develop over a period of time, it takes more surgical time, but for experienced plastic surgeons, not a complicated procedure.
The wrinkling that you have makes me think you have saline implants. I recommend silicone Memory gel implants to reduce this risk.
Thank you for your question and photos, and good luck.

If you want smaller implants, then they can be downsized. You likely need an ADM or fat grafting to camouflage the rippling that I see in some of the photos.

I am sorry to hear about your disappointment with the results of the breast surgery.Downsizing of breast implants and improvement of the breast implant rippling  revisionary breast surgery will likely involve adjustment of the breast implant capsules along with the use of acellular dermal matrix.  I would not say that it is an "easy procedure";  on the other hand, it is not a difficult procedure for a plastic surgeon who has significant experience with revisionary breast surgery.Policy regarding coverage of expenses for revisionary surgery will vary from office to office and probably on a case-by-case basis as well. Costs of revisionary surgery may range from zero,  to anesthesia/surgery center fees, to discounted surgeon's fees.Best wishes.