Is it possible to block complement activation at specific organ of the body?

It is really hard to answer your question, since it depends of what activation you would like to block. Any in particular?

Yes. I want block C4 activation. Is it possible?

You can try to create a single-chain Fv antibody against C4. It has been done for C5 see reference below. The flip side is that severe side effects might occur in vivo.

Thomas TC, Rollins SA, Rother RP et al. Inhibition of complement activity by humanized anti-C5 antibody and single-chain Fv. Mol Immunol1996; 33:13891401