You want to read M.W. Frederiksen's 1966 article "Caesar, Cicero and the Problem of Debt." Frederiksen more or less solved the question of Caesar's reaction to the "crisis of credit" in 49, particularly by identifying the lex Julia de bonis cedendis as Caesarian. Frederiksen argued (and his argument has been accepted for decades now) that Caesar introduced the custom of cessio bonorum, by which some debtors could declare their insolvency to the praetor and be allowed to cede land and goods, keeping only enough to keep themselves alive, in order to liquidate their debts. Cessio bonorum was a significant part of debt relations in the Principate, since it allowed members of the senatorial class (most of whom were debtors) to declare insolvency without suffering infamia. This, provided Frederiksen is right, is the "reform" you're talking about. More certainly attested is Caesar's response to the credit crisis in 49, which was not a reform and not intended to be lasting. In 49 Caesar ordered that property, the value of which tanks during civil war, should be assessed by creditors at its pre-war value, and revived an old law forbidding the keeping of coin over the value of HS 60.

This last is relevant, because Frederiksen's article should also correct some misunderstandings you seem to have about debt in the Republic and Caesar's response to it, none of which I have the space nor opportunity for here. In the first place debt was not a problem of the poor borrowing money, but was a question of credit--apart from farmers few of the poor had significant debts. In the second, Caesar was not responding to debt generally, but to a specific problem caused by the outbreak of the civil war. The civil war caused creditors to call in their debts very suddenly and unexpectedly, and to stop lending out coin, resulting in an acute shortage of cash and an unwillingness to extend credit. Caesar's actions in response to the crisis were aimed at releasing cash back into the economy, in particular to allow him to pay his troops--this entire episode should not be separated from the simultaneous decision on Caesar's part to confiscate the treasury illegally in order to distribute it to his soldiers.