While I understand your request, and it makes sense to me as well, this is not how many real-world flight planning systems work. If an airway switches repeatedly between east-west, as Y488 does in your example, the software will simply switch from even and odd as often as needed to respect NEODD SWEVEN on a per-leg basis.
Probably the logic is that while it’s extremely unlikely ATC will actually direct you to do this, the flight plan and fuel calculations are being more conservative by planning for this possibility. If the AIP specifically says to use a certain altitude, however, generally the AIRAC data will be coded appropriately, and so will SimBrief. But that doesn’t appear to be the case for Y488.
Different companies might use different systems, and/or their dispatchers might have internal policies or preferences to manually force certain altitudes for known problematic airways. But my understanding is that by default, the software will not use any kind of discretion or common sense on its own, and in general, we try to make SimBrief act as close as possible to the real flight planners it is based on.
For a real-world example, take a look at the flight that filed this route on FlightAware. Notice how Y488 is repeated several times in their filed route:
While FlightAware removes the actual step altitudes, repeating airways like this are a telltale a sign that this flight probably filed numerous steps on Y488.
With that said, real-world pilots also see this in their OFPs sometimes. Often they won’t bother actually inputting all of these steps into the FMC, they’ll use their best judgement to decide what the actual most likely altitude will be on that airway. The OFP is just a planning exercise, and the resulting fuel burn and time enroute will often not be significantly changed by alternating 1,000ft steps.
Here for example, I’ve forced FL350 on Y488, and it made almost no difference to the time and fuel burn:
While it’s a bit more time consuming for sure, it should really only take you an extra step, if you do it as follows:
- Finalize your payload and most other flight parameters, then use Calculate and Compare to generate a preview of your route and planned step climbs.
- Click the “Copy” button in the route box, then return to your flight options, and paste this route (which effectively bakes these step climbs into your OFP from now on). You don’t need to remove anything from it, just paste it as-is:
- Disable SimBrief’s “Stepclimbs” option to prevent any glitches and make sure it follows the baked in step climbs fully.
- Edit or delete any step climbs as you see fit, then generate.
You might already be using that trick, but if not, hopefully it can make dealing with this issue easier!
Down the road we do want to add a more user-friendly interface for editing enroute altitudes, but it’s just one of hundreds of things on our to-do list. 
Best regards,
