Putting Back the Same Implant After Capsulectomy?

WIth grade IV capsular contracture, many insurnace companies will actually pay towarsd your treatment.  I would personally perform a capsulectomy with use of new implants.  I would not use old implants again since they may harbor a biofilm of bacteria around them that can result in capsular contracture again.

The real problem is we really cannot definitively identify the cause nor can we provide a consistent recommendation regarding the management of capsular contracture.
In my mind you have a few options and of course some of this is based on my personal practice experience over 15 years now:

My most consistent and reliable method of treating capsular contracture is capsulectomy and implant replacement with a NEW implant.
Capsulotomy/partial removal and replacement with the EXISTING implant can be successful but not on a consistent basis.
Regardless of any technique capsular contracture may recur.
Cohesive gels are not available for widespread use at this time as you know. I know you are attempting to save money but you may want to consider replacing both implants with similar ones to assure a more symmetric outcome.
You may find that returning to Costa Rica is the most economical solution but there are no guarantees this will solve the problem.

In terms of mix/match it really depends how much tissue you have and how big the implants are which is difficult to guess over the internet. Let me give you an oversimplified example which provides some insight:

IF you take a football and a volleyball the difference in shape will be very obvious if you cover them with a silk sheet. Howevery you may barely notice the difference if you cover them with a thick comforter. What do you have: silk sheets or comforters?

I hope this helps!

I agree with Dr. Moelleken that any surgery around an intact implant where the end result includes having an intact implant in place should have implants available.
In my practice we believe that a major cause of capsular contracture (hard or firm breast implants) comes from subclinical bacterial contamination.
To reduce the possibility of this happening again, we would recommend the implants being replaced (the biofilm on the old implants may be impossible to sterilize). That is not to say that re-using the old implant is improper, but in our experience, it may increase the possibility of recurrent capsular contracture.
To answer your new questions - mixing the implants (as long as they are both silicone for consistent feel) should be ok. Be sure to remember that the sides may feel different even if the same implant is used because of the additional surgery on the breast with the capsular contracture. Depending on the extent of the capsulectomy - your old implant may not be enough to give you symmetry.
Be sure to discuss all these issues with your surgeon before your surgery.
I hope this helps!