To any variety $X$ over a field of characteristic zero, say $k$, one can attach a resolution of singularities, say $X'\to X$, with the following properties: 1. $X'\to X$ is an isomorphism over $X_{\mathrm{reg}}$. 2. if $\Theta:X\rightarrow Y$ is an isomorphism of schemes (not necessarily defined over $k$), then $\Theta$ can be extended to an isomorphism $\Theta':X'\rightarrow Y'$ compatible with $\Theta$ and the resolutions. It follows from 1. and 2. that if $\Psi:Y\rightarrow Z$ is a second isomorphism of schemes, then $(\Psi\circ\Phi)'$ and $\Psi'\circ\Phi'$ coincide on the inverse image of $X_{\mathrm{reg}}$ in $X'$, and hence they coincide on $X'$. With a similar argument, we have $(\mathrm{id}_X)'=\mathrm{id}_{X'}$. In particular, if $G$ is any group of automorphisms of $X$ (not necessarily defined over $k$), the action of $G$ on $X$ can be lifted to an action on $X'$. For a reference, see: O. Villamayor: Equimultiplicity, algebraic elimination, and blowing-up. *Adv. in Math.* 262 (2014) 313-369. ([ArXiv link](https://arxiv.org/abs/1312.7836), [DOI link](https://doi.org/10.1016/j.aim.2014.04.013))