Depending on the boot you can take the liner out... and have the toe box of the shell "milled" or cut out a bit to fit your toes. If you have a dremel you could try yourself. Just dremel out a small amout of pastic at a time. Put the liner back in and try them on. Repeat untill your toes arent jammed in there. Some people have irregular feet, like super wide or have a big knobber on your toe or something. If thats the case you would take them to a bootfitter and get them milled out to fit.
So, that didnt asnwer your question at all.. The liner will pack out some. I would say try to ride them a day or two, if it jacks your toes up real bad and isnt getting better after a few days I would take them to a bootfitter.