Firstly, the build up of carbon dioxide should not jeopardize the ferment in any way. In fact, it probably serves to protect your ferment further from going bad or taking a turn in the wrong direction. Lactic acid bacteria grow under anaerobic conditions (absence of oxygen) during lacto-fermentation. These are the microbes that you really want to have thriving on the fruit or vegetable in the bag. As more carbon dioxide builds up in the bag, it further inhibits the growth of other competing aerobic microbes (that require oxygen to grow) such as mould that would spoil the ferment, encouraging lactic acid bacteria to prevail and dominate.
Secondly, you should not really have too much problems with running the vacuum sealer unless there is really a huge amount of liquid. You could pour out some of the excess liquid to reduce the level in the bag before resealing. You may also try sealing with a weaker suction.
I would strongly advise against freezing and then thawing the ferment. The freeze thaw process would affect the viability of the microbes and you would end up with a handicapped ferment as some proportion of the microbial population would die off as they are being frozen. You should only freeze your ferment for storage after it has reached your desired end state.
In fact, burping is probably not necessary if your ferment progresses fast enough to reach your desired end maturity. By then you would be concluding the ferment by cutting open the bag to harvest the contents.
Ultimately, I think the purpose of burping is simply to prevent the bag from bursting due to excess gas build-up.