There shouldn't be any problems running a halogen headlight bulb if the rest of the charging system's in A1 condition. There are checks that you can do quickly & cheaply using a multimeter.
First off, check that you're getting a similar reading of about 17vac across each pair of yellow wires coming out of the alternator. If any one pair of windings is reading low then buzz out the wires using the resistance meter. All readings should read the same across any pair of yellow wires of say 5 ohms.
If the stator windings buzz out ok, then check that the rectifier output is about 15vdc, which is then mechanically regulated. The regulator can be tested & adjusted on the bench using a voltage supply after cleaning up the points under the metal cover.
While you have the resistance meter out, check that the earth leads back to the negative connector for the battery reads...to all intents & purposes...zero ohms. If it reads higher than say a few ohms, then clean the connectors of corrosion & buzz the wiring again.
On my old CB550F1 I ran twin spots via a relay from the battery without any problems. On a later CB550F2 I used the glass from a CB550K3 which had the H4 unit as standard. Later I fitted a Cibie Z beam unit that at one time had been fitted to my CB750F2 before that was converted to something else.
Check also that the battery on the 550 is good. If the bike is left unused for any length of time a cell or two of the six may well start to sulphate & short out the plates. Using an 'Optimate' trickle charger is a good investment.
