Hi! 
I would love to be able to add altitude (and / or speed?) restrictions to waypoints manually, I found that there’s currently no way to do it?
Use cases:
- During cross the pond (VATSIM event) for example a certain altitude at oceanic entry is dictated by the event coordinators. Sometimes that altitude can differ quite significantly from the altitude that is economical and therefore impacts payload / fuel calculations.
- Airport pilot briefings often suggest certain altitudes at certain waypoints for descent planning which could impact the cruise altitude.
Best wishes! 
Hi, please see the User Guide Route Formats section.
It is possible to enter custom step climbs or descents in the route using standard ICAO notation: ABC DEF/F340 XYZ
. It isn’t possible to specify a loose altitude (such as “at or below” or “at or above”) nor is it possible to modify the cruise speed.
Also note that automatic step climbs will be disabled if you enter any manual altitudes. If you’d like to take advantage of SimBrief’s auto step climbs, but also specify some manual altitudes, I recommend first generating your flight without manual altitudes to see which altitudes SimBrief selects. Then copy the route from the Flight Briefing page (which will include the inline step climbs), click “Edit Flight”, paste the copied route into the “Route” option, modify the altitudes as needed, and finally regenerate the flight.
Best regards,