Seats in the House of Commons orginally represented boroughs and towns. The Parliamentary Boundaries Act 1832 altered the district map by eliminating some boroughs and changing the number of seats in others. Had any such change ever been made before?
Until the seventeenth century there were frequent alterations, but almost all for new places to be enfranchised, which I suspect isn't the sort of change you're thinking of.
If you go back long enough, the counties were relatively stable, but the number of towns varied - for example, 88 in 1394, 81 in 1399, and 87 in 1421. By 1509, there were 98 boroughs, 37 shires, and 12 'urban counties'; Henry VIII added all the Welsh shires, of course, but even without that change, the number of seats grew steadily, and there were a third more members in 1558 than there were when he started. The odd town was dropped, as well. The overall number continued to rise until 1673, when the last constituencies were added; after that, no English constituencies changed until 1832. (The Scottish constituencies were added in 1707 and the Irish ones in 1801. I don't believe any were disenfranchised during this period.)
The one exception to this century and half of stability was the case of Grampound, in Corwall, disenfranchised by Act of Parliament in 1821 - and this can be seen as one of the early skirmishes in the approach to the 1832 reforms. You could also argue that East Retford was a disenfranchisement of sorts - in 1830 the existing tiny borough was reformed to represent the local area as a more conventional rural constituency.
There had previously been moves to disenfranchise Stockbridge (1689, 1694) and Hindon (1701), but these did not get through Parliament. The 1701 election was sufficiently corrupt that it sparked a few general reform proposals along the lines of the 1830s legislation, but, again, these didn't get anywhere.
There was a projected plan by Pitt in 1785 which fell through:
Pitt's plan now was to extinguish thirty-six of [the rotten boroughs], and to increase the representation of the counties correspondingly. London and Westminster were also to have an increase, a share in the seventy-two seats provided by the abolition of thirty-six constituencies. So far Fox and his followers were ready to support Pitt against the vested interests which were opposed to reform; but Pitt proposed to recognise those vested interests by buying them out, and to this Fox would not consent. The result was that Pitt was unable to carry the measure...