Can you change ej20 big end bearings without removing engine?

no, the crankshaft has to be removed to get to the bearings therefor removing the pullies, fan belts, timing belt, sump, main studs etc etc,

if you are considering upgrading internal bearings i recommend doing a total rebuild, eg - arp head studs and main studs, eagle rods, forged or billet items inc pistons, rods, bolts, bearings, boring if needed and nitriting the crank along with the block for strengthening,

no point in pulling a engine down just to change 2 bearings, may as well spend the time wisey and upgrade everything else at the same time.

more money yes, but a small price to pay for 4 times the power and 10 times the strength and reliability :-)