Can I vacuum-pack jars that don't seal with a new lid while they are still piping hot? If not, why not please. It seems if the tomato sauce has been simmering on the stove for hours and then boiling for 35 min. in a BWB, it should work.
The replacement of a leaking lid is fine but you do need to reprocess the contents as before. Airborne bacteria can easily contaminate the contents even if very hot, and a new lid is placed on the reopened jar. Always be sure to use new lids, allow them to sit in hot, barely simmering water, and attach to the jars after wiping the glass rims with a damp paper towel. Always tighten using the two finger and thumb strength, unless your hands are not very strong, so then you would use 3 fingers and thumb to tighten rings snugly only. Always wait for jars to cool after they have been processed before determining if seals are leaking. All new lids have a dimple that pops in slighly, and that happens when the jars are cooling. You dont usually see that when they are first removed from the canner. Be patient, for the jars that may not indicate a vacuum until nearly cooled to room temps.
You can if you wish but it sure isn't recommended for safety reasons - airborne contamination occurs and then grows while the jar is in storage.
As Ken said the jar should be reprocessed with a new lid. That is the standard guideline.
Here is a link that might be useful: NCHFP - Canning FAQs - Jar didn't seal?
No to vacuum sealing, unless you mean to just keep it in the frig and eat it in a short period of time instead of bothering to reprocess in the canner. Not safe for long storage.
That said, I sure don't use another new lid when reprocessing. I check to see if the jar has some small defect in the lip I didn't notice before. Hubby does a lot of canning, and for some reason has a lower sealing rate than I do. I don't know what he is doing wrong. He has tried screwing the rings on tighter, no help, and then tried screwing them on more loosely. Whatever, he often has a jar or two not seal in a batch. I take them apart, clean off the jar and lid and reheat the lids, and reprocess. They seal just fine.
I am thinking he maybe isn't as careful in wiping the rim of the jar before putting the lid on? We just try to have me do the lid putting on part whenever possible to avoid this problem. But I have almost never had the problem be with a new lid itself. And we can about 200 jars of stuff every year. I don't see the point of wasting good lids, they are our main expense in canning.
Of course I also reuse lids that are in great shape, and that works well, too, and I can in pickle jars and so on. You can tell if something is sealed or not, especially when you open it and hear that thunk sound of air rushing in, so I have no concerns about safety.
If the lid failed, and I didn't see any damages to the glass jar seal area, I would not reuse the lid again. Its just too risky if there was a tiny bit of something mashed into the sealing compound of the lid, that you didn't detect when examining them after reopening them. This would be typical if the jars had added dried dill weed and/or dill seeds, which can get up into the seal area. Here, I had just one single jar lid fail after doing over 500 jars in several years, and that was for a single jar of peaches which leaked out all the liquid, even though it was standing upright. It was tossed as it had been that way for quite some time.
I pull a vaccum on unseled jars but then they go into the fridge or freezer