No, you cannot convert a 10rnd. magazine into a 12rnd. magazine. The magazine bodies, locking plates, and base plates are made different on purpose so that such a thing is incapable of being done.
These are the replacement springs you may need for the 10rnd. mags.
HK 10 Round Magazine Spring - HKPARTS.NET
These are the replacement springs you may need for the 10rnd. mags.
HK 10 Round Magazine Spring - HKPARTS.NET