PEGylated lipid membrane structure and phase behavior are important areas of study because of their potential in various biochemical, biomedical, and pharmaceutical applications. Here, we study mixed bilayers of DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) and PEGylated DOPCs (on phosphorus) in water using the MARTINI coarse-grained force field and show that the self-assembled structures can be changed between micelles and bilayers by applying different isotropic and semiisotropic (i.e., surface tension) pressure conditions. Radial distribution functions as well as radii of gyration confirm that structures are distinctly different. The results indicate that environmental conditions can be used to transform, manipulate, and eventually control lipid assemblies.