Getting "list assignment out of range" error when setting variable through exec or locals()

Question

I am trying to change a variable by referring to it via a string. The problem arises, when I try to replace a variable which before was was an array with length 1 with one that is longer ("list assignment out of range" is thrown when trying to assign a value to the second array element)

I tried using locals()[variable] = [-1, -1, -1] as well as exec(variable + ' = [-1, -1, -1]') to set the variable beforehand.

My code for reference:

        exec('tmp = ' + variable)  # save variable in case input gets reset
        exec(variable + " = [-1, -1, -1]")  # replace with 3-length array
        try:
            # set the first array element according to user input
            exec(variable + '[0] = float(input("Enter lower bound for " + variable + ": "))')
        except ValueError:  # in case user is dumb
            print("Invalid input")
            exec(variable + ' = tmp')
            continue

        try:
            # set the second array element according to user input (this line throws the error)
            exec(variable + '[1] = float(input("Enter upper bound for " + variable + ": "))')
            if eval(variable + '[1] < ' + variable + '[0]'):  # more user safeguards
                print("Value can't be lower than " + str(aq_p[0]))
                exec(variable + ' = tmp')
                continue
        except ValueError:
            print("Invalid input")
            exec(variable + ' = tmp')
            continue

For some context: It's about setting up a physics simulation where a dozen parameters have to be set (and later versions may include other parameters) which is why I want to keep the code as general as possible instead of hard-coding the input for every parameter. I wanted to avoid using a dictionary with all the parameters in it, as that may complicate other things and was hoping to be able to use locals() similarly.

As a side note: The continues in the code are for a larger loop which is too long to include here.