Hey from central North Carolina U.S. In Europe, 9 mm charcoal filters are popular, but they do reduce nicotine, so you probably don't want to use them. Most filter pipes smoke just fine without the filters or adaptors. There are quite a few stronger (in nicotine) blends, and most online sources indicate strength in the specifications. i wouldn't do this with additives of any kind. MacBaren's Rustica, as recommended, is high in nic, as is Semois, the Belgium burley variant, and a number of others.
There is enough flavorful pleasure in milder blends that you might actually enjoy some of those in rotation with stronger blends.
P.S. I have a friend who retired to Stuttgart for about ten years, but returned to his home area near New Orleans, Louisianna, to be near family, and to be in his first language.