Hmm, the Fx brokers that I know all calculate profits in the same way as FXCM.

For EUR/USD, the current Pip-EUR conversion rate is 0.0800. You can normally see the conversion rate when you start your broker's platform, f.i. the FXCM trading station, and look into the currency detail view. The rate is named like "PipCost" or "PipValue" dependent on the broker.

The rate does indeed change, but infrequently. It does not follow the daily dollar price. The current value, 0.0800, was the same in 2012. So your trade had earned exactly the same 84 cents profit when you had executed it back then on a real EUR account. In 2011 the rate was lower, like 0.078.

A change of the rate does however not affect the PnL in the simulation. The simulation only uses the current pip cost, not the USD exchange rate and also not the broker's historic pip costs. Otherwise the equity curve would not reflect the performance of your strategy, but also the USD price or the broker's conversion rates.

Anyway: if you want to convert the profits of your trade to another currency at the real exchange rate, you can do that in the script. You can set PipCost to a different value, so you can use the price of an asset, f.i. EUR/USD, for calculating an artificial PipCost that changes daily.