We present an optical variability study of 44 newly identified blazar candidates behind the Magellanic Clouds , including 27 flat spectrum radio quasars ( FSRQs ) and 17 BL Lacertae objects ( BL Lacs ) . All objects in the sample possess high photometric accuracy and irregularly sampled optical light curves ( LCs ) in I filter from the long-term monitoring conducted by the Optical Gravitational Lensing Experiment . We investigated the variability properties to look for blazar-like characteristics and to analyze the long-term behaviour . We analyzed the LCs with the Lomb-Scargle periodogram to construct power spectral densities ( PSDs ) , found breaks for several objects , and linked them with accretion disk properties . In this way we constrained the black hole ( BH ) masses of 18 FSRQs to lie within the range 8.18 \leq \log ( M _ { BH } / M _ { \odot } ) \leq 10.84 , assuming a wide range of possible BH spins . By estimating the bolometric luminosities , we applied the fundamental plane of active galactic nuclei variability as an independent estimate , resulting in 8.4 \leq \log ( M _ { BH } / M _ { \odot } ) \leq 9.6 , with a mean error of 0.3 . Many of the objects have very steep PSDs , with high frequency spectral index in the range 3 - 7 . An alternative attempt to classify the LCs was made using the Hurst exponent , H , and the \mathcal { A } - \mathcal { T } plane . Two FSRQs and four BL Lacs yielded H > 0.5 , indicating presence of long-term memory in the underlying process governing the variability . Additionally , two FSRQs with exceptional PSDs , stand out also in the \mathcal { A } - \mathcal { T } plane .