I am curious if anyone uses a skiing helmet for winter biking? Would this be safe? Are skiing helmets designed to protect you from the same kind of accidents that you would have on a bike?  

My thinking is that a ski helmet would:


Help to keep your ears warm
Would fit well with ski goggles (which fit poorly with my bike helmet)
Not have air vents in it which make you cold in the winter



Question: change gb4e enumeration in only one chapter
Answer: You can simply reset the exx counter just after the \appendix command:

\appendix
\setcounter{exx}{0}


MWE (borrowed from linked answer)

\documentclass{book}
\usepackage{gb4e}

\begin{document}
\chapter{}

\begin{exe}
\ex
\gll born be?ettef\={a}q.e yek.i ?az aqv\={a}m.a\v{s} be \v{s}ahr.e per\={a}g moh\={a}jerat kard\\
     Born with.EZ one.INDEF from relatives.CL-3SG to city.EZ Prague move did.3SG \\
\glt `Born moved to the city of Prague with one of his relatives.'
\end{exe}

\begin{exe}
\ex
\gll born be?ettef\={a}q.e yek.i ?az aqv\={a}m.a\v{s} be \v{s}ahr.e per\={a}g moh\={a}jerat kard\\
     Born with.EZ one.INDEF from relatives.CL-3SG to city.EZ Prague move did.3SG \\
\glt `Born moved to the city of Prague with one of his relatives.'
\end{exe}

\chapter{}

\begin{exe}
\ex
\gll born be?ettef\={a}q.e yek.i ?az aqv\={a}m.a\v{s} be \v{s}ahr.e per\={a}g moh\={a}jerat kard\\
     Born with.EZ one.INDEF from relatives.CL-3SG to city.EZ Prague move did.3SG \\
\glt `Born moved to the city of Prague with one of his relatives.'
\end{exe}

\appendix
\setcounter{exx}{0}

\chapter{}

\begin{exe}
\ex
\gll born be?ettef\={a}q.e yek.i ?az aqv\={a}m.a\v{s} be \v{s}ahr.e per\={a}g moh\={a}jerat kard\\
     Born with.EZ one.INDEF from relatives.CL-3SG to city.EZ Prague move did.3SG \\
\glt `Born moved to the city of Prague with one of his relatives.'
\end{exe}

\end{document} 


Output: