limitfish, check the specifications for your bike and the new bulb/seal beam. If your original light and your replacement light have the same power rating in Watts (as in 40W low beam, 55W high beam mentioned earlier) then your replacement will draw exactly the same current through your wires. So there will be no difference in the power drawn from you charging system and no additional load put on the head light circuit components.
IMHO, the real question is "are your wires and especially connector contacts and switch contacts as good as they were 20-30 years ago"?
On my bike some were not. I had real switch contact problems such that the Hi and Lo beams would cut out while driving or both would come on at the same time like a strobe light. Other drivers were not amused!
Over time I had to solve this the long and hard way in 4 separate phases:
1) First, I had to disassembled and cleaned the switch contacts (don't lose that ball bearing).
2) Second, I had to check, repair and or replace the connector contacts in the head light circuit (cheap from Z1 Enterprises).
3) Third, I had to install two automotive relays into the head light circuit to keep the high current out of my weak switch gear (cheap from local auto/electronics shop). Let me know if you need the circuit diagram I used.
4) Fourth, I decided to change out the fuse box for a more modern Blade type fuse box. This last one was more of a pre-emptive strike against any future spoiled rides caused by intermittent fuse contacts. I'll never know if it was really necessary or not... and that's OK by me.
Hope this helps.
BTW, have you added your year, model and location to your signature. It's considered very friendly here and will get you the best replies.
Best of success!