MPEP 1504.04 discusses converting originally disclosed broken lines to solid lines:
"an amendment that changes the scope of a design by either converting
originally-disclosed solid line structure to broken lines or
converting originally-disclosed broken line structure to solid lines
would not introduce new matter because such amendment would not
I will just include the mandatory recommendation here to get a patent attorney. If your invention is worth protecting, it's worth protecting properly. Otherwise, you're just throwing money away at filing fees with little chance of getting something at the end.
With that out of the way...
What must a US non-provisional application ...
Is it possible to file amendments for the descriptions/drawings at the same time as entering US national phase?
Preliminary amendments can be filed when a PCT application enters the national phase in the US. This is apparent from 37 CFR 1.115, which provides:
(a) A preliminary amendment is an amendment that is received in the Office (§ 1.6 ) on or ...