etotheipi
Yes the symmetry transformation ##\delta \mathbf{r} = \delta \boldsymbol{\theta} \times \mathbf{r}## and ##\delta \mathbf{v} = \delta \boldsymbol{\theta} \times \mathbf{v}## with ##\delta \boldsymbol{\theta} = \delta \theta \mathbf{\hat{n}}## induces a change in Lagrangian of \begin{align*}
\delta \mathcal{L} = \dfrac{\partial \mathcal{L}}{\partial \mathbf{r}} \cdot \delta \mathbf{r} + \dfrac{\partial \mathcal{L}}{\partial \mathbf{v}} \cdot \delta \mathbf{v} &= \dot{\mathbf{p}} \cdot \delta \boldsymbol{\theta} \times \mathbf{r} + \mathbf{p} \cdot \delta \boldsymbol{\theta} \times \mathbf{v} \\
&= \delta \boldsymbol{\theta} \cdot \left( \mathbf{r} \times \dot{\mathbf{p}} + \mathbf{v} \times \mathbf{p} \right) \\
&= \delta \boldsymbol{\theta} \cdot \dfrac{d}{dt} \left( \mathbf{r} \times \mathbf{p} \right)
\end{align*}so letting ##\hat{\mathbf{n}}## be arbitrary implies ##\dfrac{d}{dt} \left( \mathbf{r} \times \mathbf{p} \right) = 0##. Of course, if the angular momentum about ##O## is ##\mathbf{L}_O = \mathbf{r} \times \mathbf{p}## then about some axis ##(O,\hat{\mathbf{n}})## you may write\begin{align*}
\mathbf{L}_O \cdot \hat{\mathbf{n}} = \mathbf{r} \times \mathbf{p} \cdot \hat{\mathbf{n}} &= \hat{\mathbf{n}} \times \mathbf{r} \cdot \mathbf{p} \\
&= |\mathbf{r}| \sin{\varphi} \hat{\boldsymbol{\phi}} \cdot \mathbf{p} \\
&= \rho \hat{\boldsymbol{\phi}} \cdot \mathbf{p}
\end{align*}where ##\rho = |\mathbf{r}| \sin{\varphi}## is the distance from the axis ##(O,\hat{\mathbf{n}})## to the particle and ##\hat{\boldsymbol{\phi}} \cdot \mathbf{p}## is the azimuthal component of the momentum; ##\mathbf{L}_O \cdot \hat{\mathbf{n}} ## is also an integral!
\delta \mathcal{L} = \dfrac{\partial \mathcal{L}}{\partial \mathbf{r}} \cdot \delta \mathbf{r} + \dfrac{\partial \mathcal{L}}{\partial \mathbf{v}} \cdot \delta \mathbf{v} &= \dot{\mathbf{p}} \cdot \delta \boldsymbol{\theta} \times \mathbf{r} + \mathbf{p} \cdot \delta \boldsymbol{\theta} \times \mathbf{v} \\
&= \delta \boldsymbol{\theta} \cdot \left( \mathbf{r} \times \dot{\mathbf{p}} + \mathbf{v} \times \mathbf{p} \right) \\
&= \delta \boldsymbol{\theta} \cdot \dfrac{d}{dt} \left( \mathbf{r} \times \mathbf{p} \right)
\end{align*}so letting ##\hat{\mathbf{n}}## be arbitrary implies ##\dfrac{d}{dt} \left( \mathbf{r} \times \mathbf{p} \right) = 0##. Of course, if the angular momentum about ##O## is ##\mathbf{L}_O = \mathbf{r} \times \mathbf{p}## then about some axis ##(O,\hat{\mathbf{n}})## you may write\begin{align*}
\mathbf{L}_O \cdot \hat{\mathbf{n}} = \mathbf{r} \times \mathbf{p} \cdot \hat{\mathbf{n}} &= \hat{\mathbf{n}} \times \mathbf{r} \cdot \mathbf{p} \\
&= |\mathbf{r}| \sin{\varphi} \hat{\boldsymbol{\phi}} \cdot \mathbf{p} \\
&= \rho \hat{\boldsymbol{\phi}} \cdot \mathbf{p}
\end{align*}where ##\rho = |\mathbf{r}| \sin{\varphi}## is the distance from the axis ##(O,\hat{\mathbf{n}})## to the particle and ##\hat{\boldsymbol{\phi}} \cdot \mathbf{p}## is the azimuthal component of the momentum; ##\mathbf{L}_O \cdot \hat{\mathbf{n}} ## is also an integral!