are partially filled bottles ok?

So few things going on here.

1. Over carbonation : It sounds like you over carbonated your porter in the keg. Porters are at the low end of the carbonation spectrum usually about 1.5 - 2.0 volumes. That excessive foam you got I doubt was from temperature differences. More likely the carbonation level. If you did a white (milk?) porter it would have been very sensitive to carbonation level.

2. Residual Carbonation : if the liquid foams heavily before settling it means much of the gas is expelled in that process. I can’t tell from your post if you left the bottles half full or gradually filled. Either way the excessive foaming will result in the liquid holding onto less gas.

3. Bottle Volume: Recall from (1) that a porter needs a bottling volume of gas of about 1.5-2.0. But that the mix of that gas was expelled during bottling. This means that what ever is left in the liquid is all that there is to pressurize with. Meaning much of the liquids gas will be lost to the bottle until it equalizes. This could result in an under carbonated beer.

So,

• If you left your bottles half full and capped like that, I’m 99% sure they will be heavily under-carbonated. Too much will be lost to the bottle. However;
• If you did fill the bottle before capping you stand about a 65% chance of the carbonation still being okay (not great) Why? Because you made a porter which is by its type low in the fizzy spectrum. (So maybe your choice of beer saved you.)

Good luck.