As a Brit, but not a teacher, I would advise as follows:
Rushing "pell-mell" into something means rushing:
pell-mell: Definition and Much More from Answers.com
re: "Keeping your matchlock lit", you are correct in your assumption that it means: "Be ready at all times" i.e. it can be used metaphorically, outside its original context.
- In a jumbled, confused manner; helter-skelter.
- In frantic disorderly haste; headlong: “I went to work pell-mell, blotted several sheets of paper with choice floating thoughts” (Washington Irving).rushing into doing something, regardless of any possible consequences.
See Matchlock - Wikipedia, the free encyclopedia for details of matchlocks (note: it's a single word rather than match lock)
Also see: Keeping your matchlock lit: Web Search Results from Answers.com
An inherent weakness of the matchlock was the necessity of keeping the match constantly lit.
Hope this helps
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